Is the MIDI 5-pin DIN to TRS cable wired using the MIDI type-A wiring where Tip is connected to pin 5, Ring is wired to pin 4, and sleeve is wired to pin 2?

What messages have you programmed the GCX buttons to send? Are you sure the GCX is sending on channel 1 and the MicroPitch is receiving on CH1? have you tried setting the EXP input to MIDI Box instead?