Setting Gain On Hifonics Bxi1208d

[eliassami5]

Ive got two Dual 4 ohm subs wired down to a final load of 4ohms following RF's wiring wizard. My amp puts out 750 wats at 4ohms, so using the formula [volts=square root (amp power x ohm load)] so [square root (750x4)=54.xx]. But when i go and try to set the gain on the amp with my DMM, the highest voltage the amp will produce is 48ish even with the bass knob turned all the way to max and the gain up to the max and the bass bost up to max. Am i supposed to half the voltage that i got from the formual? since the HiFonics Brutus 1208D is a mono amp but has two positive and negative terminals for subs to be plugged into.

I have the DMM leads on the terminals that are marked with yellow, but it dosent make a difference if i put the leads on the other terminals