First buy the Mach 3. The G540 has an outut that ouputs a 0-10 vdc control signal. The pot on your spindle now just varies the voltage (0-10v most likely), you will run the output of the G540 to the same connections as your speed pot is connected to now. First you would have to verify your voltages on the pot. Measure the output of thepot as you rotate the knob. Does it vary between 0 & 10v?