I just finished installing a 4 channel amp into my car and I can only get 2 channels to work. I have a skar audio RP-75.4AB 500w amp, and a pioneer s322bt head unit. In addition to that i have a 2 channel amp running a sub. I have been using the head unit to power the 4 door speakers but it did not have the power necessary to do so. It has 2 sets of rcas one for the sub and a second I ran back to the skar amp and split it to hook up to the 4 channels. after doing so the amp would play out of to speakers no matter what configuration i moved the rca inputs to, sometimes it only played out of 1 speaker. The rca output on the head unit is for full range front speakers is that the problem am I not able to split it to run both front and back speakers?