R56 owners who are doing turbo-back exhaust mods might be interested in talking with Mike or Bill at Sweet Thunder. They will do custom work using their chambered mufflers. Here's what it could look like (with different heat shields of course):

 

Wow... that looks really sweet Give us some more details, sound, performance, etc...

 

Sweet Thunder (out of MI) make these chambered mufflers in stock sizes and custom (mine are 14" custom--about the smallest they make.) The set up you see uses a 2.5" core in the center tunnel then splits to the 2x 2" cores before the tips. The external diameter is about 1" larger than the cores, but still smaller than a traditional muffler. I got aluminized steel, but they will make them in 304 Stainless at 1.5x the price.
I will post some audio, but your Turbo cars would sound a lot different to my SC car, especially as I have a custom CMC header which uses non-standard cylinder pairing. (Not that that matters with a turbo, I guess !)

 

how bout a straight on rear shot?

 

btw, it's for sale. Contact me.

 

reminds me of a fast intentions exhaust (FI) ....mmmh this sound is SEX:
(i used to own an audi, hush for the non-mini content)
http://www.youtube.com/watch?v=LqEqXckkBKA

 

mmmm B5 S4's are the best!

I'm an Audi guy too