Im having the hardest time trying to have both sets or rca preouts from the back of the head unit to be on full with no subwoffer.. i have one 4 channel amp controling 4 spkrs but only the front work and im getting a low "(subwoffer buzz)" sound comming from the rear spkrs.. anyone please tell me to change the settings to make it make it front and rear..?? i have the manual and i cant understand how its trying to help me fix my issue.