1999 Suburban 6 speaker wiring

I have a 1999 Suburban with the factory 6 speaker stereo.  It has the front door speakers, rear door speakers, and 2 more in the headliner by the back doors.  I installed a new head unit using the Metra wiring plug, i connected the wires as indicated.  now the front doors are on the front channels of the head unit and the rear channel controls the rear headliner spakers.  Absolutley nothnig from the rear doors.  I was wondering how to hook up the ear door speakers, or maybe wire the rear door and the headliner speaker in series on each channel for rear fill. Any ideas would be great.

there's a factory amp in that truck.. it is going to be on the right of the steering wheel under the dash.. you will want to rewire it.. colors to connect as follows

red to dk blue, tan to lt blue, white to brown, tan to yellow...

one thing to watch for it that there are TWO tan wires.. make sure you are pairing up the right tan wire with the right speaker + lead.. the tans are -... just get a battery and pop the  speakers and connect accordingly.. the brown and yellow are one channel and the blue and lt blue are the other..

if I have totally confused ya.. just post or email.. later