That is the setup I have in a 318 coupe!
2 X Alpine 10" subs in boot run by a 200w Alpine Amp
Two Alpine 4" Mids in foot well and two Alpine Tweeters in front door all run by a 400w Alpine Amp
Nakamichi crossover controlling the whole lot.
I disconnected the rear speakers from BMW as they were struggling over the subs and removed them and the plastic box mounts to allow the sound through the rear parcel shelf!
Sounds awesome unless you are sitting in the back and then it sounds like just a tonne of bass - but I sit in the front so who gives!?!
<img src='http://img.photobucket.com/albums/v629/BLACKBMW1/alssig.jpg' border='0' alt='user posted image' />
Thought for the day: "d'uh"