OP, you need to at least include this link:
http://www.wheelsto.com/servlet/the-...-E92-M3/Detail
They have a system exhaust, where you can easily bolt on the Clubsport exhaust for the street and then the Motorsport one for the track if you want a dual system. I don't know loud the Motorsport one is, but the Clubsport isn't too loud, but offers a nice rumble.