please help i am trying to hook this 4 channel amp to 2 1300 watt sony subs. i have started out bridging 1 sub with the gain down low and increasing slowly and it seems to be no output. i have set the amp rear output to LPF instead of full and i am not using the front out put at all. do i have to use all inputs and outputs on this amp to make it work? (note) I do have power to the amp and no fuses have popped.