No other hardware is required except spindle control if you need it. I have no idea what type of machine you have. Mine is a retrofitted Bridgeport CNC Mill. I'm using the PMDX-107 spindle controller (PWM signals to my VFD) mounted to my PMDX-126 as well. Note, the 126 can supply 5v power to ONE, either the ESS or the 107 but not both. In that case you would need an extra power supply, which can be a simple AC-DC adapter.
The only issue I had with Mach 4 & ESS was the homing offset, which Daz has created a work around for. My X and Y +/-/home limits are all on the same switch and was having troubles sometimes when I hit the switch, limit over ride wouldn't work backing off them. I had to manually disassemble some things and turn my ball screws off them. Since the new version of Mach 4, I haven't had any more problems.
Royce