I know many members here eventually end up upgrading their cd players when they upgrade their stereo system, but it really is not necessary. Originally the problem I ran into when I installed amplified speakers all around, while keeping the original deck, was that the speakers distorted HEAVILY even when turning the bass very low. I think many others experienced examples of bad sound quality while keeping the stock deck. After tuning and adjusting my stereo equipment yesterday for three hours I was able to get good sound out of the stock deck. It does take work, but it is possible. The sound is damn near close what it sounded like with my aftermarket pioneer cd player. It still has the annoying bass boost at low volumes, but it'* not staticy, nor does it distort at all.
The way I setup my system is I used the speaker leads for the front speakers, used a LOC and ran the RCA'* to the back. From there, the RCA'* connect to my rear speaker'* amplifier, then the RCA out from that amp connects to the amplifier for my front speakers. Basically, both run off of the front c hannel of the headunit. I used the rear channel, and another LOC, to run my Infinity Basslink in the trunk. I set it up this way so that I could use the fader on the headunit to adjust how loud the bass is, or none at all, from the basslink, while still having the door/rear deck speakers still play the same ammount of bass regardless. It also makes listening to distortion easier because with just using the fader, I can listen to ONLY the basslink play to listen for distortion, and tunen it, or I can listen to only the full range speakers without the basslink playing.
To take care of the distortion problems I was having, I had to set the gain slider on the LOC'* to almost the bare minimum. Before, I had the gains on the amps set pretty low, and the LOC'* around the center. However, anything above 25% on the LOC'* caused distortion. I ended up raising the gains slightly on the amplifiers, and having the gain on the LCO'* VERY low. I now don't have any of the distortion problems I had before. To further protect my full range speakers, I set my amps to have a crossover point of 100 HZ. My full range speakers do not play under 100HZ and the basslink takes care of any signals under 100 HZ. I set the gain on the basslink lower because the bass was way too heavy from the stock deck.
After many adjustments, and playing with different crossovers, settings, and gain settings, I was able to get fantastic sound out of the stock deck. There is no static, or dead noise unless it is cranked. (but even aftermarket decks can do that.) Basically, fi you want to keep your stock cd player regardless of the reason, it IS possible to get good sound out of it. It just takes quite a bit of work..
If you're really ambitious, you can even add an EQ, or EQ/DSP to enhance and tune the sound even further. I may or may not go this route to further enhance the sound quality. If I do that, I'll be doing it this spring when it'* not so damn cold outside.
Hopefully this is helpful to someone else too. If you have any other questions, let me know!