Why do you feel the need to increase amp gains and reduce signal into the amp? (You can get the same power but reduce noise in the system also) That’s not a good gain structure, reset the gains at minimum and increase signal in, you should always reduce gains first not signal in to get the signal to noise of the system as good as can be
its easy to do, just use a multimeter, measure at a set head unit level the output of the amp, then reduce gains and then increase signal from the dsp until the voltage matches once more, simple