The USBIO unit allows you to control relays and read switches via gcode. I don't think that is what you want.
By far the easiest way to get functions that have a keyboard shortcut (CycleStart, Reset, etc) is via a keyboard emulator. You use an Arduino or Teensy or... to make PP think that you have typed whatever on the keyboard. I have been happily using such for years on my 770. The best part is that no changes to PP are required; it just works. Total parts cost is perhaps $25. I wrote an article for Digital Machinist magazine that provided detailed instructions and there is other material online.