Terry I wouldn't buy Smooth stepper or anything yet because chances are your problems are not with the parallel port but the TB6560 or some thing else.

What is the problem exactly.?

Excuse if you know this but let me explain how typical setup goes.

PP --> BOB --> Drive --> Motor

Parallel port(PP) sends/recieves signals to Breakout Board (BOB) which then Sends pulses to individual Drive for each motor, It also recieces signals from outside sources like E-stop or limits etc.

All the Smooth stepper does is remove the parallel port from the equation. It's great piece of kit and recommended thing to buy but not yet because like as been said you probably don't need it.

For less than price of ESS you'll buy 3 new Digital drives, Cheap BOB and PSU that will blow the Tb6560 out the water and turn your mill into all new animal even with the PP.!!