This is a message I received from Scott at Mach Support:
The only time you should see a voltage change for the axes is on the direction pints when they change direction - unless you are looking at the pulse train with an O-scope, you will not see any voltage change on the step pins. If you are seeing inputs activate when you ground pins, though, I do not think you are having a problem with Mach outputting signals - the driver either works or it does not, if you can see inputs it is sending outputs. My question to you would be does that breakout board need or expect a Charge Pump signal, and if so do you have it configured? The motors are getting power, but do they need any sort of an Enable signal before they will run? Also, you may need to adjust the pulse width of your step and direction signals (which you can do in Motor Tuning), depending upon how sensitive your drives are...
I am not sure if the C10 board requires a charge pump signal to run.