I have a 2012 Honda civic Si with a Nav head unit. I recently purchased two Audison amps (SR1DK & SR4). AS per the attached sketch CarStereo.pdf I have 4 speaker outputs from the head unit which I wired to the speaker inputs on the SR4 and then wired the outputs directly to the speakers. First problem is the system has very low volume. Second problem is I have no more outputs available for the SR1DK which drives the subs. How do I split the outputs or is there a better way using the pre-in and pre-outs on the amps?