Ok so at one ohm that amp makes 1200 watts RMSx 1 channel,
What your gonnna need to do is download a test tone off limewire or somthing in the 50-60hz area, disconect the subs from the amp, reset all the settings on the head unit so theres nothing on Ie bass or anything like that.
put your leads of the multi meter on the speaker terminals and set the meter to read volts, turn the gain on the amp all the way down, now turn up the head units volume to about 60-70 percent, start turning up the gain screw on the amp the meter reads 34.64 volts,
34.64 =1200 watts