If I were you I would take my time and read as many of the threads related to changing head units here as possible.(do a search for head units here)
Also you need to establish which system you have and what options
you have attached to the head unit such as SOS, bluetooth etc..
http://www.e90post.com/forums/attach...2&d=1266451970
http://www.e90post.com/forums/showthread.php?t=352586
http://www.e90post.com/forums/showthread.php?t=343673
http://www.e90post.com/forums/showthread.php?t=321871
http://www.e90post.com/forums/showthread.php?t=365866
There are few shops even good ones that can do a e90 series 3 correctly
The three stereo models are stereo(non US model except for 2010 2011) , HI Fi or premium, L7 or logic 7
they all have the professional head unit in the US.
Also I seem to recall someone mentioned the 330 came with logic 7 standard
in 06 which would mean the amp and speakers would have to be replaced probably
with and ms-8 some amps and speakers.