The C controller has a pwm output that can be used as an input for a speed controller of a DC motor, and with 100% pwm as an input for on-off swith. A second output is 1-10V and needed when you use a VFD spindle controller.
Thanks Martin. Yes, found that topic and ordered from Automation Technologies. Already have the spindle in hand and building the x-carve this week.
I think you could save a few bucks ordering the same parts from Chinese suppliers, but I read good things about customer support from Automation Technologies and figured that if there is any issue with either the VFD or spindle, I would rather deal with them.