I've heard people suggest setting the gains with a DMM and 50hz test tone. But I've heard other people say that doing that will make it not sound as good. I just kind of put on something and set the gains to a point where it doesn't distort anymore and have my sub level on my HU at -10 (goes from +6 to -24). Then I can go up or down from there, usually around -8 with the gain a little less than half. Like one notch down from half. The xover past half way (I use the LPF on my head, so I figure the one on the amp is useless.) And the bass boost just over half (a little past one notch up from half)
Also, I don't really know how to use the dadgum multimeter... I mean, kind of but not really. And I don't know how to generate a 50hz tone or if it would be better to use say a 30hz tone.