[FormerRotor]

VASTYLE, let us know how te Renntech tune goes. From everything I've heard, his is an excellent option as long as you don't mind the price tag.

I wouldn't worry about exhaust, etc. until you've exhausted the ECM options. Because of the way our (I drive a 335d) exhaust systems are laid out--DPF, urea injection, etc.--you would have to go completely custom (as of today) and may very well have to bypass the emissions equipment to see any worth-while gains. There are muffler options, but these really don't seem to be the restriction on our Diesel systems, and even removing the mufflers (only) all-together won't give you the significantly louder exhaust note you may expect(if your going for sound).

Some have replaced the piping from the DPF back with custom mandrel-bent for fewer turns & crimps and gone with resonators instead of mufflers. They state they can feel more exhaust (as in the hand by the exhaust pipe method) but noted that the sound change was negligable and have not mentioned any performance gains. There's a place in Elkridge, MD with some experience if you want to go this route

Keeping an eye on the e90 diesel forums may be a good idea.