Have you checked out http://www.pac-audio.com?
They have AUX adapters for all manner of stereos, including stock/factory units. They would be a likely source for what you need.
Hi guys I searched the forums and did not find, so I will ask. My stock head unit (Delphi XTA-2300 ) has cd changer support. Any Idea where I find the output schematic for it? O woils like to run through the stock stereo. Not like you need more in this tank. lol. any help would be great. thanks