I have a JL Audio 12W6 & JL 500/1 mono amp hooked up to the factory CD unit. I wanted to retain the factory steering wheel control and factory CD changer. It sould great. The JL audio amp have a remote Bass control which is mounted in the ash tray. Lot of Bass.
The amp also have Hi level input so I cut off one end of the RCA cable and solder the wires to the rear RS speaker from inside the trunk. It a Mono amp so i don't care about R or L input. The sound in the cab area are clear and the Bass are awersome
Later I will have the stereo shop build me a amp rack that fit inside right side pocket area and the subwoofer enclosure in the left side pocket and relocate the factory CD changer, the two box will flush with the trunk. These two area are dead space which I don't use for anything. That way i cna utilized the trunk space and access the spare tire if needed.