i have installed several systems but never on a stock headunit. my friend is going to be getting a 12" and a amp. he has a 2005 expedition. i told him id install it. but how exactly would i wire up the rca's or the high power input? and the remote power on wire? he has a lil stock amp pushing like a 6.5 or something like that. could i tap into that??? it is the in dash 6 disc changer if that matters.