1. Hook up your amps' power, ground, remote, and RCA cable hook-ups. (NOTE: Your sub is not required for this procedure!)
2. Follow Gain-Setting Tutorial for both amplifiers to set the gains nominally. (after this step you will only be changing the gains a very small fraction of a turn)
3. Now the voltages at each amp's speaker leads should be the same while the HU is playing the 40hz tone.
4. Turn HU down to about 50% of the full volume and ensure that the amps still read the same voltage at the speaker terminals. They should be pretty close, if not perfect. If one is different than the other, turn whichever is highest down. (have steady hands!!)
5. Turn HU down to about 25% of full volume, and set your DMM so that you have two decimal places (#.##) and check to see that the voltages are the same. They should again be pretty close, and again if one is different turn the highest down.
6. Now you are done tweaking gains. Now it is time to check crossover frequencies. Basically both amps should put out the same voltage at any given frequency. So, you can check whichever frequencies you want, just adjust the crossover so that when you play a 20, 30, 40, 50, 60 hz tone, both amps give the same amount of voltage.
GL HF, ask if you have any ?'s