So, i'm looking at rca cables right now, and if i'm going to run the PHD's with the amp running bridged/2ch, do i still need 4ch RCA's, or just RCA's for the front channel? Also, being that i'm going to put my amp under my rear seat, do you think a 4m cable would reach, or a 6m cable, and is it bad if i have slack to coil it?