I can get you my 2.1 xml later today. I was fiddling with mine - I had to set the PWM base frequency (Config->Ports/Pins->Spindle) to 1000Hz (which contradicts the mach3 documentation, which says set it around 5 or 10, and caused either off or fullspeed spindle operation for me) and min freq to 0%. After that, gcode "S" commands seem to work, numbers between S800 and S7000 will change the speed (S7000 will run the spindle faster than S6000, despite it being a "6k spindle" ). I don't have a tach to calibrate though.
I have to CD300 (cheapo) controller.