What generation (by original controller model) is your NH? Are you using it as a 3 axis machine where your active axis are X, Y and Rotary with the regular Z being controlled by the pneumatic piston?
What is the current and voltage capacity of the Xenetech electronics? My, somewhat educated, guess is that the NH steppers probably want about 3 amps and 30 Volts. If you have much less than that available, you may be skipping steps or your motors may not be holding properly when stopped.