Mitchell, Check this out. I remembered seeing a post from a guy that had the same idea. He had the SS cat-less mid pipe and the Magnaflow system. The only difference is that he had a shop weld the smaller diameter pipe on the magnaflow to the larger SS pipe. You can see it in the pictures.
http://www.1addicts.com/forums/showp...&postcount=215
I preferred to keep it modular, so expanding the one pipe on the Magnaflow allows me to take it apart later, if I need to. This makes it easier to do other work in the future.
I don't use my 128i as a daily driver, so I have plenty of time to work on it in my shop. Also, working on my car is one of my past-time hobbies. I even enjoyed drilling out the broken studs on the exhaust flange. I completely understand if you wish to avoid all that, but I will encourage you to attempt it yourself. It is really not too hard.
Best of luck!