you have to make sure both coils are getting the same amount of power (not just setting the gains the same either, it takes the math to do this), . . . . setting the gains are going to be difficult because you have a few deciding factors like how many audio input volts each amp is given (if you're running both sets of RCA's from the headunit or if you are running one set from the headunit and the other to a 'Pass Thru' on the amp, because the 'Pass Thru' outputs are amped so it's easier to hit your dedicated voltage than opposed to running it through an RCA output on the headunit.)