The theory behind matching amp gain and head unit pre out lol. Alright so here is how it goes, lets say you have a 6 volt headunit, and the amp gain range is from 6 to .2 like your amp is. The theory is you wouldn't have to adjust your gain only because you hu is 6volt out and the amp gain at the lowest setting is a 6. Now lets say you had a 4 volt out headunit you would have to adjust the gain closer to that .2 side of things because your headunit is lower voltage than the lowest amp gain setting at 6 volts. That is the theory behind everything. It was more confusing trying to type this than talking about it. I might just make a youtube video it would be easy to explain. But there is no better way to set gains than with a oscope or dd1 Oh and on the amp gain/hu matching ordeal you reach full rms power once the amp and headunit is matched for voltage.