I'm going to be bridging a 4-channel amp into 2-channels for my subs...I have no problem with the speaker wiring...my question is to I have to use RCA Y-cables at the amp or can I just input the RCA's from the HU as such...left output into channel 1 & right output into channel 3?...don't want to buy y-cables if I don't have to...also don't want to need them and not have them after the car is all apart.