I just bought a 91 s5 recently and the rear speaker enclosure and the speaker isnt there. I searched, looked for images, and looked on ebay without success or true confirmation on this matter as if a rear factory amp does not exist with s5s. My s4 gxl had the enclosure with the factory amp built in it. Can anyone answer my question? I've heard it could be mounted behind the dash as well. If that's the case then I'll just hook up some rear speakers. I've been on the forums for 15 years and this is my first s5.

 

The wiring diagram for the "Type 4" audio system does not call out a rear amplifier, only the amplifier in dash for the door speakers.