I see Vital Systems has an MPG they list for the controller.  It pretty expensive.

I also see MPG's on Ebay but not sure if they are compatible with the DSPMC controller. 

Does anyone know what the specs are to be compatible?

You can use usb type mpg, but the hand wheel click response is not very good.  If you connect mpg handwheel to any of the encoder channels, you will get quick response to hand wheel motion.  For the axis selector and gain, you can tie the buttons to any digital inputs on DSPMC and map those in mach3/mach4 to perform the desired operation.

Thank you very much for your response.  I really appreciate it.