I am almost done with my mach3 transition to mach4 with a ESS and PMDX upgrade along the way. The final piece of my puzzle is spindle speed control with PWM. When I map 'motor on' in the ESS setup and in the Mach4 config, the spindle turns on and off. When I map 'spindle pwm' (there is no Mach4 mapping) in the ESS config, the pin is always 0v. If you are using PWM to control your spindle, I would love to see your ESS and Mach configs around these particulars.

Happy Making

Did you ever solve this? Looks like I might have the same problem.