Ok, so My headunit has 3 sets of 4v outputs two(front and rear) go to the xo which is a ppi frx 456 seems to have a maximum output of 8v. My nine.5's gain control says 8v-0.3v. My other amps just say min-max. So do I adjust/match input voltage to head unit's 4v output or to the xo's 8v output. I usually just go by ear but I want to be sure that I dont clip my amps. Any HELP would be appreciated. thank you.