http://www.e90post.com/forums/forumdisplay.php?f=27
For a one stop solution go to these guys
http://www.musicarnw.com/page-2/
The following are some examples of there systems
http://www.e90post.com/forums/showthread.php?t=495855
http://www.e90post.com/forums/showth...ighlight=level
http://www.m3post.com/forums/showthread.php?t=540446
I just got through doing a DIY install with one of there kits. (about a couple of weeks ago)
These guys can set you up with a kit that suits your tastes.
They really know these cars and what works in them so the biggest mistake you can make with them is not taking there advice totally and absolutely.