Grand Prix

Sorry but no it is not possible to use the factory CD changer with an aftermarket stereo.  Some german-made vehicles have radios built by panasonic/alpine/pioneer, and a few of them use the same protocols that the aftermarket units use.  Thus for those vehicles you can sometimes use an aftermarket stereo and keep the factory changer. But there are no GM's that are like this.

Just out of curiosity, why exactly do you want to add an aftermarkt cd-player when there's already the cd changer?  Is it so that you can play mp3 cds or something like that?

Just FYI they do make adapters that let you add auxiiliary audio inputs to the factory stereo in GM cars.  The one you'd want is the PAC AAI-GM9.  It has a switch that lets you select whether you want to hear the cd's in the cd changer, or the audio from the auxilliary input.  If you had a portable mp3 player or something like that it could be hooked up to those aux inputs.

My parents like the changer, but they'd also like to have a cd player up front in case they want to "change on the fly" while on the highway.  The deck they have is the tape deck w/t graphic eq.  An aftermarket would also give them more flexibility in adjusting the 3-amp system I gave to them after my own upgrade (i.e. like the Kenwood System E+'s).