Is it only the Eisenmann Race mufflers...or the x-pipe and the mufflers?
People always say the exhaust will "break in" and get a little louder over time, but I've never really experienced that and had one change very much over time, and I've had lots of different exhausts on different cars.
In my opinion the biggest change will be from the first 10 miles to the next 300 miles.
When I put the Britalman system on (x-pipe and mufflers) my E39 M5 I noticed that the sound did change some after the first 300 miles because the inside of the pipes got sooted up...the sound changed slighty to a richer toned sound.
Hope this helps.
Oh, by the way...awesome car! A new E60 M5 with Eisenmann and 20" Radenergies! Sweet!
Photos?