diff --git a/Marlin/src/gcode/control/M350_M351.cpp b/Marlin/src/gcode/control/M350_M351.cpp
index 68e49ee50b..7fab861b65 100644
--- a/Marlin/src/gcode/control/M350_M351.cpp
+++ b/Marlin/src/gcode/control/M350_M351.cpp
@@ -27,35 +27,45 @@
 #include "../gcode.h"
 #include "../../module/stepper.h"
 
+#if NUM_AXES == XYZ && EXTRUDERS >= 1
+  #define HAS_M350_B_PARAM 1  // "5th axis" (after E0) for an original XYZEB setup.
+  #if AXIS_COLLISION('B')
+    #error "M350 parameter 'B' collision with axis name."
+  #endif
+#endif
+
 /**
  * M350: Set axis microstepping modes. S sets mode for all drivers.
  *
  * Warning: Steps-per-unit remains unchanged.
  */
 void GcodeSuite::M350() {
-  if (parser.seen('S')) LOOP_LE_N(i, 4) stepper.microstep_mode(i, parser.value_byte());
-  LOOP_LOGICAL_AXES(i) if (parser.seen(axis_codes[i])) stepper.microstep_mode(i, parser.value_byte());
-  if (parser.seen('B')) stepper.microstep_mode(4, parser.value_byte());
+  if (parser.seen('S')) LOOP_DISTINCT_AXES(i) stepper.microstep_mode(i, parser.value_byte());
+  LOOP_LOGICAL_AXES(i) if (parser.seen(AXIS_CHAR(i))) stepper.microstep_mode(i, parser.value_byte());
+  TERN_(HAS_M350_B_PARAM, if (parser.seenval('B')) stepper.microstep_mode(E_AXIS + 1, parser.value_byte()));
   stepper.microstep_readings();
 }
 
 /**
  * M351: Toggle MS1 MS2 pins directly with axis codes X Y Z . . . E [B]
  *       S# determines MS1, MS2 or MS3, X# sets the pin high/low.
+ *
+ *       Parameter 'B' sets "5th axis" (after E0) only for an original XYZEB setup.
  */
 void GcodeSuite::M351() {
+  const int8_t bval = TERN(HAS_M350_B_PARAM, parser.byteval('B', -1), -1); UNUSED(bval);
   if (parser.seenval('S')) switch (parser.value_byte()) {
     case 1:
       LOOP_LOGICAL_AXES(i) if (parser.seenval(AXIS_CHAR(i))) stepper.microstep_ms(i, parser.value_byte(), -1, -1);
-      if (parser.seenval('B')) stepper.microstep_ms(4, parser.value_byte(), -1, -1);
+      TERN_(HAS_M350_B_PARAM, if (bval >= 0) stepper.microstep_ms(E_AXIS + 1, bval != 0, -1, -1));
       break;
     case 2:
       LOOP_LOGICAL_AXES(i) if (parser.seenval(AXIS_CHAR(i))) stepper.microstep_ms(i, -1, parser.value_byte(), -1);
-      if (parser.seenval('B')) stepper.microstep_ms(4, -1, parser.value_byte(), -1);
+      TERN_(HAS_M350_B_PARAM, if (bval >= 0) stepper.microstep_ms(E_AXIS + 1, -1, bval != 0, -1));
       break;
     case 3:
       LOOP_LOGICAL_AXES(i) if (parser.seenval(AXIS_CHAR(i))) stepper.microstep_ms(i, -1, -1, parser.value_byte());
-      if (parser.seenval('B')) stepper.microstep_ms(4, -1, -1, parser.value_byte());
+      TERN_(HAS_M350_B_PARAM, if (bval >= 0) stepper.microstep_ms(E_AXIS + 1, -1, -1, bval != 0));
       break;
   }
   stepper.microstep_readings();
diff --git a/Marlin/src/gcode/feature/L6470/M906.cpp b/Marlin/src/gcode/feature/L6470/M906.cpp
index f89fe8b927..26c637df27 100644
--- a/Marlin/src/gcode/feature/L6470/M906.cpp
+++ b/Marlin/src/gcode/feature/L6470/M906.cpp
@@ -25,7 +25,7 @@
 #if HAS_L64XX
 
 #if AXIS_COLLISION('I')
-  #error "M906 parameter collision with axis name."
+  #error "M906 parameter 'I' collision with axis name."
 #endif
 
 #include "../../gcode.h"
diff --git a/Marlin/src/gcode/feature/trinamic/M569.cpp b/Marlin/src/gcode/feature/trinamic/M569.cpp
index f4c4967142..44675a850e 100644
--- a/Marlin/src/gcode/feature/trinamic/M569.cpp
+++ b/Marlin/src/gcode/feature/trinamic/M569.cpp
@@ -25,7 +25,7 @@
 #if HAS_STEALTHCHOP
 
 #if AXIS_COLLISION('I')
-  #error "M569 parameter collision with axis name."
+  #error "M569 parameter 'I' collision with axis name."
 #endif
 
 #include "../../gcode.h"
diff --git a/Marlin/src/gcode/feature/trinamic/M919.cpp b/Marlin/src/gcode/feature/trinamic/M919.cpp
index 6f3dcf729a..fa349e7f16 100644
--- a/Marlin/src/gcode/feature/trinamic/M919.cpp
+++ b/Marlin/src/gcode/feature/trinamic/M919.cpp
@@ -25,7 +25,7 @@
 #if HAS_TRINAMIC_CONFIG
 
 #if AXIS_COLLISION('I')
-  #error "M919 parameter collision with axis name."
+  #error "M919 parameter 'I' collision with axis name."
 #endif
 
 #include "../../gcode.h"
diff --git a/Marlin/src/gcode/motion/G5.cpp b/Marlin/src/gcode/motion/G5.cpp
index 316a59b650..c47f443d41 100644
--- a/Marlin/src/gcode/motion/G5.cpp
+++ b/Marlin/src/gcode/motion/G5.cpp
@@ -25,7 +25,7 @@
 #if ENABLED(BEZIER_CURVE_SUPPORT)
 
 #if AXIS_COLLISION('I') || AXIS_COLLISION('J')
-  #error "G5 parameter collision with axis name."
+  #error "G5 parameter 'I' or 'J' collision with axis name."
 #endif
 
 #include "../../module/motion.h"
diff --git a/Marlin/src/module/stepper.cpp b/Marlin/src/module/stepper.cpp
index 6c552959ee..60eb635965 100644
--- a/Marlin/src/module/stepper.cpp
+++ b/Marlin/src/module/stepper.cpp
@@ -3679,7 +3679,7 @@ void Stepper::report_positions() {
   void Stepper::microstep_ms(const uint8_t driver, const int8_t ms1, const int8_t ms2, const int8_t ms3) {
     if (ms1 >= 0) switch (driver) {
       #if HAS_X_MS_PINS || HAS_X2_MS_PINS
-        case 0:
+        case X_AXIS:
           #if HAS_X_MS_PINS
             WRITE(X_MS1_PIN, ms1);
           #endif
@@ -3689,7 +3689,7 @@ void Stepper::report_positions() {
           break;
       #endif
       #if HAS_Y_MS_PINS || HAS_Y2_MS_PINS
-        case 1:
+        case Y_AXIS:
           #if HAS_Y_MS_PINS
             WRITE(Y_MS1_PIN, ms1);
           #endif
@@ -3699,7 +3699,7 @@ void Stepper::report_positions() {
           break;
       #endif
       #if HAS_SOME_Z_MS_PINS
-        case 2:
+        case Z_AXIS:
           #if HAS_Z_MS_PINS
             WRITE(Z_MS1_PIN, ms1);
           #endif
@@ -3714,52 +3714,52 @@ void Stepper::report_positions() {
           #endif
           break;
       #endif
-      #if HAS_E0_MS_PINS
-        case  3: WRITE(E0_MS1_PIN, ms1); break;
-      #endif
-      #if HAS_E1_MS_PINS
-        case  4: WRITE(E1_MS1_PIN, ms1); break;
-      #endif
-      #if HAS_E2_MS_PINS
-        case  5: WRITE(E2_MS1_PIN, ms1); break;
-      #endif
-      #if HAS_E3_MS_PINS
-        case  6: WRITE(E3_MS1_PIN, ms1); break;
-      #endif
-      #if HAS_E4_MS_PINS
-        case  7: WRITE(E4_MS1_PIN, ms1); break;
-      #endif
-      #if HAS_E5_MS_PINS
-        case  8: WRITE(E5_MS1_PIN, ms1); break;
-      #endif
-      #if HAS_E6_MS_PINS
-        case  9: WRITE(E6_MS1_PIN, ms1); break;
-      #endif
-      #if HAS_E7_MS_PINS
-        case 10: WRITE(E7_MS1_PIN, ms1); break;
-      #endif
       #if HAS_I_MS_PINS
-        case 11: WRITE(I_MS1_PIN, ms1); break
+        case  I_AXIS: WRITE(I_MS1_PIN, ms1); break
       #endif
       #if HAS_J_MS_PINS
-        case 12: WRITE(J_MS1_PIN, ms1); break
+        case  J_AXIS: WRITE(J_MS1_PIN, ms1); break
       #endif
       #if HAS_K_MS_PINS
-        case 13: WRITE(K_MS1_PIN, ms1); break
+        case  K_AXIS: WRITE(K_MS1_PIN, ms1); break
       #endif
       #if HAS_U_MS_PINS
-        case 14: WRITE(U_MS1_PIN, ms1); break
+        case  U_AXIS: WRITE(U_MS1_PIN, ms1); break
       #endif
       #if HAS_V_MS_PINS
-        case 15: WRITE(V_MS1_PIN, ms1); break
+        case  V_AXIS: WRITE(V_MS1_PIN, ms1); break
       #endif
       #if HAS_W_MS_PINS
-        case 16: WRITE(W_MS1_PIN, ms1); break
+        case  W_AXIS: WRITE(W_MS1_PIN, ms1); break
+      #endif
+      #if HAS_E0_MS_PINS
+        case  E_AXIS: WRITE(E0_MS1_PIN, ms1); break;
+      #endif
+      #if HAS_E1_MS_PINS
+        case (E_AXIS + 1): WRITE(E1_MS1_PIN, ms1); break;
+      #endif
+      #if HAS_E2_MS_PINS
+        case (E_AXIS + 2): WRITE(E2_MS1_PIN, ms1); break;
+      #endif
+      #if HAS_E3_MS_PINS
+        case (E_AXIS + 3): WRITE(E3_MS1_PIN, ms1); break;
+      #endif
+      #if HAS_E4_MS_PINS
+        case (E_AXIS + 4): WRITE(E4_MS1_PIN, ms1); break;
+      #endif
+      #if HAS_E5_MS_PINS
+        case (E_AXIS + 5): WRITE(E5_MS1_PIN, ms1); break;
+      #endif
+      #if HAS_E6_MS_PINS
+        case (E_AXIS + 6): WRITE(E6_MS1_PIN, ms1); break;
+      #endif
+      #if HAS_E7_MS_PINS
+        case (E_AXIS + 7): WRITE(E7_MS1_PIN, ms1); break;
       #endif
     }
     if (ms2 >= 0) switch (driver) {
       #if HAS_X_MS_PINS || HAS_X2_MS_PINS
-        case 0:
+        case X_AXIS:
           #if HAS_X_MS_PINS
             WRITE(X_MS2_PIN, ms2);
           #endif
@@ -3769,7 +3769,7 @@ void Stepper::report_positions() {
           break;
       #endif
       #if HAS_Y_MS_PINS || HAS_Y2_MS_PINS
-        case 1:
+        case Y_AXIS:
           #if HAS_Y_MS_PINS
             WRITE(Y_MS2_PIN, ms2);
           #endif
@@ -3779,7 +3779,7 @@ void Stepper::report_positions() {
           break;
       #endif
       #if HAS_SOME_Z_MS_PINS
-        case 2:
+        case Z_AXIS:
           #if HAS_Z_MS_PINS
             WRITE(Z_MS2_PIN, ms2);
           #endif
@@ -3794,52 +3794,52 @@ void Stepper::report_positions() {
           #endif
           break;
       #endif
-      #if HAS_E0_MS_PINS
-        case  3: WRITE(E0_MS2_PIN, ms2); break;
-      #endif
-      #if HAS_E1_MS_PINS
-        case  4: WRITE(E1_MS2_PIN, ms2); break;
-      #endif
-      #if HAS_E2_MS_PINS
-        case  5: WRITE(E2_MS2_PIN, ms2); break;
-      #endif
-      #if HAS_E3_MS_PINS
-        case  6: WRITE(E3_MS2_PIN, ms2); break;
-      #endif
-      #if HAS_E4_MS_PINS
-        case  7: WRITE(E4_MS2_PIN, ms2); break;
-      #endif
-      #if HAS_E5_MS_PINS
-        case  8: WRITE(E5_MS2_PIN, ms2); break;
-      #endif
-      #if HAS_E6_MS_PINS
-        case  9: WRITE(E6_MS2_PIN, ms2); break;
-      #endif
-      #if HAS_E7_MS_PINS
-        case 10: WRITE(E7_MS2_PIN, ms2); break;
-      #endif
       #if HAS_I_MS_PINS
-        case 11: WRITE(I_MS2_PIN, ms2); break
+        case  I_AXIS: WRITE(I_MS2_PIN, ms2); break
       #endif
       #if HAS_J_MS_PINS
-        case 12: WRITE(J_MS2_PIN, ms2); break
+        case  J_AXIS: WRITE(J_MS2_PIN, ms2); break
       #endif
       #if HAS_K_MS_PINS
-        case 13: WRITE(K_MS2_PIN, ms2); break
+        case  K_AXIS: WRITE(K_MS2_PIN, ms2); break
       #endif
       #if HAS_U_MS_PINS
-        case 14: WRITE(U_MS2_PIN, ms2); break
+        case  U_AXIS: WRITE(U_MS2_PIN, ms2); break
       #endif
       #if HAS_V_MS_PINS
-        case 15: WRITE(V_MS2_PIN, ms2); break
+        case  V_AXIS: WRITE(V_MS2_PIN, ms2); break
       #endif
       #if HAS_W_MS_PINS
-        case 16: WRITE(W_MS2_PIN, ms2); break
+        case  W_AXIS: WRITE(W_MS2_PIN, ms2); break
+      #endif
+      #if HAS_E0_MS_PINS
+        case  E_AXIS: WRITE(E0_MS2_PIN, ms2); break;
+      #endif
+      #if HAS_E1_MS_PINS
+        case (E_AXIS + 1): WRITE(E1_MS2_PIN, ms2); break;
+      #endif
+      #if HAS_E2_MS_PINS
+        case (E_AXIS + 2): WRITE(E2_MS2_PIN, ms2); break;
+      #endif
+      #if HAS_E3_MS_PINS
+        case (E_AXIS + 3): WRITE(E3_MS2_PIN, ms2); break;
+      #endif
+      #if HAS_E4_MS_PINS
+        case (E_AXIS + 4): WRITE(E4_MS2_PIN, ms2); break;
+      #endif
+      #if HAS_E5_MS_PINS
+        case (E_AXIS + 5): WRITE(E5_MS2_PIN, ms2); break;
+      #endif
+      #if HAS_E6_MS_PINS
+        case (E_AXIS + 6): WRITE(E6_MS2_PIN, ms2); break;
+      #endif
+      #if HAS_E7_MS_PINS
+        case (E_AXIS + 7): WRITE(E7_MS2_PIN, ms2); break;
       #endif
     }
     if (ms3 >= 0) switch (driver) {
       #if HAS_X_MS_PINS || HAS_X2_MS_PINS
-        case 0:
+        case X_AXIS:
           #if HAS_X_MS_PINS && PIN_EXISTS(X_MS3)
             WRITE(X_MS3_PIN, ms3);
           #endif
@@ -3849,7 +3849,7 @@ void Stepper::report_positions() {
           break;
       #endif
       #if HAS_Y_MS_PINS || HAS_Y2_MS_PINS
-        case 1:
+        case Y_AXIS:
           #if HAS_Y_MS_PINS && PIN_EXISTS(Y_MS3)
             WRITE(Y_MS3_PIN, ms3);
           #endif
@@ -3859,7 +3859,7 @@ void Stepper::report_positions() {
           break;
       #endif
       #if HAS_SOME_Z_MS_PINS
-        case 2:
+        case Z_AXIS:
           #if HAS_Z_MS_PINS && PIN_EXISTS(Z_MS3)
             WRITE(Z_MS3_PIN, ms3);
           #endif
@@ -3874,29 +3874,47 @@ void Stepper::report_positions() {
           #endif
           break;
       #endif
+      #if HAS_I_MS_PINS
+        case  I_AXIS: WRITE(I_MS3_PIN, ms3); break
+      #endif
+      #if HAS_J_MS_PINS
+        case  J_AXIS: WRITE(J_MS3_PIN, ms3); break
+      #endif
+      #if HAS_K_MS_PINS
+        case  K_AXIS: WRITE(K_MS3_PIN, ms3); break
+      #endif
+      #if HAS_U_MS_PINS
+        case  U_AXIS: WRITE(U_MS3_PIN, ms3); break
+      #endif
+      #if HAS_V_MS_PINS
+        case  V_AXIS: WRITE(V_MS3_PIN, ms3); break
+      #endif
+      #if HAS_W_MS_PINS
+        case  W_AXIS: WRITE(W_MS3_PIN, ms3); break
+      #endif
       #if HAS_E0_MS_PINS && PIN_EXISTS(E0_MS3)
-        case  3: WRITE(E0_MS3_PIN, ms3); break;
+        case  E_AXIS: WRITE(E0_MS3_PIN, ms3); break;
       #endif
       #if HAS_E1_MS_PINS && PIN_EXISTS(E1_MS3)
-        case  4: WRITE(E1_MS3_PIN, ms3); break;
+        case (E_AXIS + 1): WRITE(E1_MS3_PIN, ms3); break;
       #endif
       #if HAS_E2_MS_PINS && PIN_EXISTS(E2_MS3)
-        case  5: WRITE(E2_MS3_PIN, ms3); break;
+        case (E_AXIS + 2): WRITE(E2_MS3_PIN, ms3); break;
       #endif
       #if HAS_E3_MS_PINS && PIN_EXISTS(E3_MS3)
-        case  6: WRITE(E3_MS3_PIN, ms3); break;
+        case (E_AXIS + 3): WRITE(E3_MS3_PIN, ms3); break;
       #endif
       #if HAS_E4_MS_PINS && PIN_EXISTS(E4_MS3)
-        case  7: WRITE(E4_MS3_PIN, ms3); break;
+        case (E_AXIS + 4): WRITE(E4_MS3_PIN, ms3); break;
       #endif
       #if HAS_E5_MS_PINS && PIN_EXISTS(E5_MS3)
-        case  8: WRITE(E5_MS3_PIN, ms3); break;
+        case (E_AXIS + 5): WRITE(E5_MS3_PIN, ms3); break;
       #endif
       #if HAS_E6_MS_PINS && PIN_EXISTS(E6_MS3)
-        case  9: WRITE(E6_MS3_PIN, ms3); break;
+        case (E_AXIS + 6): WRITE(E6_MS3_PIN, ms3); break;
       #endif
       #if HAS_E7_MS_PINS && PIN_EXISTS(E7_MS3)
-        case 10: WRITE(E7_MS3_PIN, ms3); break;
+        case (E_AXIS + 7): WRITE(E7_MS3_PIN, ms3); break;
       #endif
     }
   }