I'm ditching the entire system: head unit, speakers, and amp. My question is about the head unit, I need a factory adapter for the head unit I know, but I'm curious if I need the Axxess GMOS-01 (gmos01) OnStar Interface for Non-Amplified GM or the Axxess GMOS-04 (gmos04) OnStar Interface for Amplified GM Systems. Any other advice from someone who has done this before would be great! Thanks!