Do you have some other way of testing your MIDI in port? Do you have a MIDI interface for your computer (rather than using the USB connection to the M3)? If you have any other gear that can send MIDI notes through the MIDI in port on your M3 then you should be able to easily verify whether or not the port is the problem.
Also, have you verified that the Triton MIDI out is actually sending the notes? Again, if you have a MIDI interface or some other MIDI gear then you should be able to test that as well.
Also, if you want to test your M3 at GC remember that you only have to take in the module... a lot easier than taking in your whole keyboard.
