You need this.... http://www.installer.com/item/displa....php?it=sni-15
brown wires tap to a ground. the whites and grays connect to rear speakers. i know on this forum that wiring diagrams are listed so you can find that with a search. but once you hook those in behind the radio, plug in your rca's from your amp to this converter.
Problem solved. Just did this in my tahoe and it sounds very clean. Dont cheap out to much on the converter. The one i listed is my favorite for that price range. Any audio shop will have one like it or similar.
post back if you have any questions.