Hi,
I couldn't see anything wrong with the jumper settings. The fact it works when the axes are not moving indicates that it is unlikely to be the DigiSpeed. If the system is generating sufficient noise to interfere with the PWM signal to the DigiSpeed, then that is an issue that should be addressed. Without an oscilloscope to see what is going on with the PWM signal from Mach3, it is very difficult to determine the cause of the problem.
Do you have an index sensor connected? And do you have spindle closed loop control selected. If so this be causing a problem.
In the end, if you can't get it to work, or are not happy with it, return it and I will refund the cost of the DigiSpeed.
Cheers,
Peter