I'll start with 2500mm/min for Z in Motor Tuning.
I still have MaxPath42, which seems to be a MaxNC renamed Mach3 version R3.033. I'll reinstall it and see if it makes a difference. Might make the A channel work.
Yes, the actual board is a 10108C, not A, but I looked for differences and could not find them.
As it is almost impossible to read the part numbers on the .doc, I could not verify if there had been a part update.
I have not been able to find a circuit diagram for my C model.