Going to bridge my amp to 3 channels, do I plug in channel 3 and 4 with the rca cables or just channel 3. I am running the rear off channel 1+2, then 3+4 channel will be bridged for a sub. The amp can be bridged and the speaker wire connections are drawn on the amp, but I dont know if you still need to connect 3+4 as the speaker gets bridged between left and right, so in theory 3+4? I am confused...help would be great please