my .02
gains are not volume controls!
you said you have 4 gauge wire to the amps - bet you did nothing to upgrade your battery to ground! or alt to ground.
do you know how to use a volt meter? - what loads are your amps seeing? are they rated for that?
these are basic installer rules to follow - if dont know, pay someone who does and save your equiptment - in the long run your system will sound better - louder and last longer!