I would suggest reading through the n55 section on this forum and trying to contact a guy called Justin from MHD. Unsure on his username, but I keep reading lots of positive things on his custom tunes.
Now I'm not sure if he needs your car, or whether he can tune from logs, but he may be able to help if you have a general chat about next steps and explain your concerns.
FYI - These are where I do most of my reading on my commute to work. The US generally seem ahead and more fbo guys over there.
http://www.e90post.com/forums/forumdisplay.php?f=375
http://www.n54tech.com/forums/forumdisplay.php?f=16
Good luck and do keep us posted!