Bastards, I was LIED to......unbeliveable.
To be fair to the dealerships.. I believe the regular 3's with the 6 disk changer get MP3 support.. but for some reason the MS3 didnt... the dealership probably just assumed that the top of the line model had the top of the line stereo... you should inform them that they are incorrect in their assumption...
... and then make them get you the mp3 changer (approx $600 I believe).