2000 audio upgrade - help with rear speakers

[Mangosmoothie]

I believe I the m490 option - dash speakers, door speakers, rear speakers, DSP controls. Car currently has single din Kenwood HU. The rear speakers are not working at all

I ordered power acoustik single din car play

Kicker KSC40 for the dash and included metra pnp harness

Metra 70-1787 for head unit and included crutchfield diagram.


I've gathered from searching the rear are run off the head unit itself not the amp. I'm totally new to car audio and don't understand what I'm really doing. I've seen to replace the amp with a 996 6 channel and run it off that. I guess I can run it off the head unit itself, I could run 1 speaker off each head unit output? FL FR RL RR, that would be each of the 4 speakers. How would I do this using the factory harness if I go that route? what output do I hook that up to on the receiver?