mixing extruder trouble - marlin / mega / ramps / reprap x3 expander (no replies)

mixing extruder trouble - marlin / mega / ramps / reprap x3 expander

Who's got experience with mixing extruder settings? I'm setting up a 5 stepper mixing head. Started with a re-arm board but had to backtrack to mega because it seems it cannot support the x3 expander that I'm utilizing to drive the additional extruder motors.

I'm working with Marlin 2.0 / arduino / mega / ramps / reprap x3 stepper expander. I'm working on getting 5 extruder steppers to function as a mixing extruder - all 5 steppers rotate correctly in the positive - but E2 does not rotate backwards - it I tell it to go backwards it actually goes forwards (not reversed - only turns one direction regardless of positive or negative commands). Everything works on my machine except for one of the mixing steppers does not understand how to turn backwards. Wiring checks out, and the stepper driver checks out (I've tested these by swapping components to different axis).

The appropriate changes have been made to my pins.h file, I think:

#ifndef E2_STEP_PIN
#define E2_STEP_PIN 64
#endif
#ifndef E2_DIR_PIN
#define E2_DIR_PIN 59
#endif
#ifndef E2_ENABLE_PIN
#define E2_ENABLE_PIN 44
#endif
#ifndef E3_STEP_PIN
#define E3_STEP_PIN 40
#endif
#ifndef E3_DIR_PIN
#define E3_DIR_PIN 63
#endif
#ifndef E3_ENABLE_PIN
#define E3_ENABLE_PIN 42
#endif
#ifndef E4_STEP_PIN
#define E4_STEP_PIN 57
#endif
#ifndef E4_DIR_PIN
#define E4_DIR_PIN 1
#endif
#ifndef E4_ENABLE_PIN
#define E4_ENABLE_PIN 58
#endif

I'm pretty baffled at the moment... any help would be greatly appreciated.