I have been following all the testing and info on this problem. I might be able to help you direct to the problem.
There is a buffer-driver chip on the MPC-03 card. I would expect that one of the output pins is damaged. This pin is a direct connect to the "step" command on the stepper motor amplifier. Bad step pin ..... No motor movement.
I am sure that the MPC-03 card is out of production for a few years. If you can't get this card working, finding a new MPC-03 card will be nearly impossible.
A last ditch attempt for a dumb fix.... Check the 80-pin cable to see if you have bent any pins while connecting/reseating the MOC-03 motion card.
thanks ,
Ray Scott