Radio wiring diagrams

Hi there,

I am looking to install a aftermarket subwoofer in the car listed above SX Turbo with Navi and Harmon Kardon system. I am currently tapped into the rear trunk sub via LOC, but I would like to get rid of that setup if I can find a unamplified audio source possibly leading to the stock amplifier on the right rear trunk area. I have only seen wire diagrams of the speaker wiring from that amp but none of any audio signal going to the amp.

Anyhow, I am looking for a wire diagram for behind the head unit or wires leading to the rear amp, I prefer getting the audio from the rear amp as this would be the easiest.