does the amp have high level inputs? i ran my amp for off the stock wiring and stereo for a year. had no problem with the sound. i just spliced into the wiring coming off the stock head unit.
But i have since replace my head unit with one that has RCA outs.
Im not a fan of the stock head unit and the business model was out of my price range. bought a head unit with lights that matched the stock lights almost perfectly for 120 and the harness adapter for 12 and some change. works great.