You have a MicroProto 2000 or 3000? The controllers on those are fine and should work as is with Mach. If there is any part numbers or such on it (or post a picture) someone might be able to tell you what it is.
If you need to replace it look at using a Gecko G540. They are a nice 4-axis stepper driver that is a great match for the Taig:
http://cnczone.com/products3.aspx . I'll be releasing a complete 4-axis drive box using a G540 in the next few weeks as well.