I was getting a bit confused about this as well, when I was looking at the Zapp site earlier (and especially as I haven't found decent English documentation for these devices). Thanks for the additional info.
One more question, though - when these boards talk about PWM spindle speed control, I am assuming that they have some kind of PWM->true analogue converter on board, which takes a PWM speed signal from Mach3 and gives a 0-10V (usually) signal that connects directly to the VFD. Is that right? Nothing else needed for Mach3 spindle speed control?

- Brian