I don't know about your driver boards, but the Geckos I'm using have a Disable pin, which I've set up to the Amplifier Enable output from EMC.
EMC also accepts a signal on any of the input pins, wire one to ground through a normally-closed pushbutton switch, select it in Stepconfig as an e-stop input, and check the Invert box, so the LACK of signal (depressed button or broken wire) triggers an e-stop.
According to the EMC integrator manual, remote-triggered E-stops like that will still require a press of the keyboard E-stop to reset.
Just this weekend I was able to setup the speed controller card from CNC4PC. Now, using my Sherline spindle motor and controller card (a KBLC card, like so many people use) I have speed selection and on/off control.
The speed controller from CNC4PC is the "C6" card, and REQUIRES a separate 12volt power supply, and a breakout board with buffered outputs.
A year ago I tried using the C6 on my Xylotex-driven mill, ignored the bit about using as isolated power supply, and burned up both the C6 and my mill's motor controller card. I was able to tune the system to within 10 rpm of commanded speed, anywhere from 50 to 3000 rpm... which should prove handy on a lathe.