That main board looks like a proprietary job. To be honest, I'd scrap it and assume using MACH3 and a BOB to the existing stepper drivers via level shifters as previously discussed or to new drivers & Steppers. With the standard software you start the run on the PC but nothing happens till you press the green 'cycle' button on the lower left of the panel. Obviously the panel could be rewired to input into Mach3 - e-stop, jog, etc...