Well I do have a long way to go before I get to chipping the car, for now I would want to concentrate of the other stuff. Can you tell me something about the K&N air filter I linked from ebay in an earlier comment?
I found this company called Akrapovic, here is a link of an exhaust on the 335i, too bad they do not make one for the Z4, this thing has a killer sound!!!!
Actually, on the Supersprint website there is a muffler with dual pipes which I believe is for the 06-08s, it is after all in the category saying: BMW Z4 Roadster / Coupé LHD 3.0si (265 Hp) '06 –›, so I reckon it should fit. Here is a link for the category, you can see the dual pipe muffler on the second row down:
http://www.supersprint.com/USP0000bmwZ46.asp