It all depends on which year you have, and which stereo.
For 1997-2002 it’s easy, you can buy an aftermarket head unit and install. With those years however it’s trickier if you have Bose as aftermarket HUs can introduce sound quality issues trying to work with Bose.
If, like me you have a 2003/04 with Bose then you’re SOL with aftermarket unless you did like I did and install a MOST-compatible bluetooth receiver, or the $1300 Porsche PCCM+ touchscreen unit. IF however you don’t have Bose (no door speakers) you can still install an aftermarket HU. But 03/04s without Bose are less common.
Double DIN is straightforward, just need the correct adapter kits and have to move the HVAC panel to the lower console. but again if you have a MOST fiber optic car, you’re limited - UNLESS you want to completely replace the Bose amp, speakers, and some wiring.
More wrinkles:
- DSP, yes/no?
- Know your radios: CDR220, CDR23, CDR24 etc
- PCM 2.1? factory navigation?
Best bet is to know what options/year you have and target specific searches around that.