CDR23 Stereo Upgrade
 

I have a 03 Boxster with the standard CDR23 stereo/CD with dash speakers only. I am wanting to replace the OEM dash speakers and add door speakers keeping the factory head unit. Can this be done?
Does the base unit come with an amp that would support adding after market speakers?
Is there anything unique about the base CDR23 system that would not support adding an amp and new dash and door speakers?
Since my car did not come with door speakers can these be added without major modifications to the door panel?
I am simply trying to upgrade the sound quality without spending a fortune.

Unfortunately, there's plenty that prevents you from easily doing this. I didn't think any US Spec cars came without door speakers, but if that's the case, the only viable way to change that is to get new door panels. Now, regarding the CDR23 in an 03 or newer car: your head unit to amp connection is optical, via what Porsche calls the MOST bus. You cannot install an aftermarket amp if you want to keep the factory head unit. Further, if your car really didn't come with door speakers, your amp doesn't have enough channels to drive them in the first place.

With respect to the speakers, the factory stuff uses a bit of a weird impedance, so while you could install aftermarket drivers, the amp may not be happy driving them (keep in mind the factory amp is horrendously underpowered in the first place).

Unfortunately with these cars, audio upgrades are pretty much an all or nothing type deal. That said, you can do a whole aftermarket setup for fairly reasonable money, that will sound WORLDS better than what you have now.

CD23 Upgrade
 

Thanks for the info. Any suggestions on an after market set-up at a reasonable price? I would like it to blend as well as possible with the OEM stereo as far as lighting and size. I am just looking for better sound quality without having to make a major investment.

Like cloudsurfer said, any sort of upgrade is basically a complete overhaul which is new stereo, amp and speakers (plus all new wiring) which means $$$.