[ctuna]

Sounds like your dealer doesn't know his product or there is a lack
of technical knowledge somewhere.
The tweeter and 4 inch in the door are connected in parallel.

BMW stereo types
http://www.e90post.com/forums/showthread.php?t=352586
http://www.e90post.com/forums/attach...2&d=1266451970
http://www.e90post.com/forums/attach...2&d=1260829447
http://www.e90post.com/forums/showthread.php?t=343673
http://www.e90post.com/forums/showthread.php?t=138949
http://www.e90post.com/forums/attach...2&d=1260829447
http://www.e90post.com/forums/attach...1&d=1209780605
http://www.e90post.com/forums/attach...1&d=1209780865
http://www.musicarnw.com/page-2/
http://www.e90post.com/forums/attach...4&d=1278871872

Look at these for detailed info there is a block diagram in one of these for
Hi Fi

Read the audio upgrade start here thread for upgrade solutions.
this one
http://www.e90post.com/forums/showthread.php?t=641323