I see many posts and itis a huge world of Audio in Cars. I have been in it and deep since 1973. Yes, alot has changed, but always for the new improved vehicles we drive. I love becker radios and they follow the same with the VW, Por, BMW and Mercedes vehicles. In my daighters Mercedes 300E 1999, it has a later Fiber Optic Mercedes Becker. It has custom 8" Klipsch woofers rear, 4" mid range and 4" tweeters in the rear, all Klipsch with similar set-up in the front. Also linked a 100 amp Fiber optic amp. and I made custom grills(painted to match) and it rocks.
Getting back to Porsches, early units of the water cooled on out have it set up to use analog pre-amp inputs or fiber optics. First is the D2B loop and next came the MOST link, witch incorporated steering wheel controls, traffic and weather systems and linked external preamping. We now have a WORLD of awesome speakers (I like JBL) amps, thermal cooling for amps and the rest is more more more!
I will include some pics, because a great instal always looks factory installed. More to come!!!

10 Po Becker CD linked with a 2 ch and a 4 ch JBL amps, same location as the 6 channel factory amp. Carefully wired in with gold connectors and hand made shielded leads.

JBL woofer/tweeter withCustom wiring harnesses all phased. No adapters, hand machined into factory housings.
With JBL crossover package.

Ya, it is time consuming, however, needed to rewire correctly with a factory 6 speaker system!