You said earlier that pressing +/- did make the speed change just did it slowly???
Is that the case?
If yes them Mach IS controlling your speed, its just not set right, if NO then you have more work to i'm afraid.
All my code will (should) do is to start your spindle and send it to max speed, nothing else, just wanted to gain an idea of your spine speed control ramp-up setting.
The last bit of code should simply turn the spindle off.