Re: Running amp through back speakers
Better off with a new head unit... But if you are dead set on not getting one, you have to use a line-out converter (LOC). You crimp the LOC onto the speaker wires. It shouldn't affect the sound you hear coming from the rear speakers, either.
Source: Pioneer DEH-80PRS
Front stage: PHD FB6.1 Pro & Vifa XT25BG60-04 on a Kenwood XR-4S
Sub stage: 2 Tantric HD12's on an Autotek MM 4000.1d
Electrical: 310 amp (lol...) Singer Alternator, 2 Wėrker 125ah batteries in back, +/- runs in Monster Cable 1/0