I went to Mikes Muffler in El Monte months ago and told him about the exhaust mod, he did a 335 before but never touched an m3.
Mike is a really cool dude, I showed him the pictures and told him how to do it and said I could go anytime and he would do it.
I went yesterday to drop off my muffler for him to work on it, they did a really good job on the whole thing, I would recommend this shop (my body shop even recommended me to Mikes Muffler) to anybody who want to do the oem exhaust mod locally.
I took my car to his shop to install it back for me since I felt like driving my car to his shop with no exhaust (was extremely loud lol) and I wanted him to listen to the exhaust he modded. All I can say is.. Wow this is the best and cheapest mod you can do for your car. I can really hear the v8 roar.
What's funny is I got a lot more head turns from my exhaust mod then when I was driving with no exhaust on lol.
The one thing I really like is that I found out its impossible to weld the bottom of the pipes together unless you open up both top and bottom part of the exhaust, and other places want to charge you extra/won't weld the bottom and leave a gap in the pipes if it isint flush, but mike did it with no extra charge.