I can only speak for the 1991 SL, as that is what I drive. As posted above, the radio electronics is in the trunk on the driver side and powers the mid speakers in the doors and the tweeters in the dash. In the console is a cassette / tuner control which feeds and controls the radio in the trunk. Under the seat is a higher power amp to run the woofers in the doors. There are no factory speakers in the rear. 6x9's can be mounted in the lids of the storage compartments, but I used 10 inch round woofers. I surface mounted a set of coaxial mid / tweeters on the "back wall" at ear lever. There is plenty of room in the storage compartments to add power amps if you want them. Here's the rub. There are no after market speakers which can fit in the doors in place of the originals. Fortunately the originals are decent quuality. The wiring on the original system is very "distributed". I decided to leave it alone and re-wire for my new system. That way I can restore the original if necessary someday. A standard DIN hole in the console will accept any DIN aftermarket radio. The system connectors are strictly Mercedes, but you can buy adaptor kits. Tod

__________________
Resistance is Futile.