Hi Finrod,

The System 3 will not be powerful enough for the 3Nm steppers, I know because I asked Roy at DIYCNC. You really need to be looking at the kit from Zapp Automation (Driver Kit 1) for your application.

I bought the Optoport from DIYCNC, really nice fully opto-isolated breakout board with charge pump and spindle/coolant relays onboard.

I bought the Driver1 kit from Zapp, 3x MDS 542 drivers which are superb, 2 PSU's which will give you enough reserve power to add a 4th axis in the future (like I will) and 3X3Nm Nema23 frame steppers. Can't recommend Zapp highly enough or Roy at DIYCNC, both have been very helpful.

For USB, you really need to look at a Smoothstepper which will run with Mach3. Just plugs into yout breakout board and that's all there really is to it. Bruce Miranda on this site was selling one up to a couple of days ago, drop him a PM see if it is still available. Gary at Zapp also said he was considering importing them. I imported mine from the USA and it cost about £120 with taxes etc.