I am by far no expert installer, but I've done a few basic setups. I'm still learning stuff. I've seen something that I've never seen before. The rear of my deck has a pair of RCA pre-outs for a front amp as well as a rear amp, but there is only ONE pre-out connection for a sub amp. What's this all about. Would I use a "Y" type connector or would I plug in the white cable or the red cable? Thank you!