Sub and Amp wiring

Just bought a 2002 Avalanche, z66 pkg (single disc), and I am wanting to wire up my amplifier and subs. How can I do so with the wiring on the avalanches?

I am keeping the stock head unit. I have the RCA line converter output to run to the trucks speakers, but I would like a way around that, due to them being in the doors. Any help would be appreciated.