[ctuna]

There are all kinds of solutions
From most peoples perspective its OK . Its what I call the almost adequate system but it shouldn't be in 50k plus car.

Weak bass and treble it falls apart with any volume and it has
big frequency hole in the middle.

Read these

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...1&d=1209780605
http://www.e90post.com/forums/showthread.php?t=641323
http://bmwcoders.com/forum/3-er-8/bm...1-e92-e93-291/
http://www.e90post.com/forums/attach...1&d=1209780865
http://www.google.com/url?sa=t&rct=j...,d.cGU&cad=rja
http://www.musicarnw.com/page-2/
http://www.e90post.com/forums/attach...4&d=1278871872

Generally a level one fix will run you around 1k in parts minimum.
A really awesome fix will run you 1.5 to 2k in parts
and you can get real ridiculous from there.
Most all upgrades will beat the HK l7 system for impact and dynamics.
Best System examples
http://www.e90post.com/forums/showthread.php?t=445266
http://www.e90post.com/forums/showthread.php?t=822366
http://www.e90post.com/forums/showthread.php?t=826683
http://www.1addicts.com/forums/showthread.php?t=634957
http://www.e90post.com/forums/showth...ight=processor
http://www.e90post.com/forums/showthread.php?t=727760
http://www.e90post.com/forums/showth...ighlight=level
http://www.e90post.com/forums/showthread.php?t=590420
http://www.e90post.com/forums/showthread.php?t=581379
http://www.e90post.com/forums/showthread.php?t=451941
http://www.e90post.com/forums/showthread.php?t=540954
http://www.e90post.com/forums/showthread.php?t=324214
http://www.e90post.com/forums/showthread.php?t=495855
http://www.e90post.com/forums/showth...hlight=technic
http://www.e90post.com/forums/showth...ghlight=Dotech
http://www.e90post.com/forums/showth...&highlight=BSW
http://www.diymobileaudio.com/forum/...morel-jbl.html
http://www.e90post.com/forums/showthread.php?t=494299
http://www.bimmerfest.com/forums/sho...d.php?t=550771
http://www.m3post.com/forums/showthread.php?t=540446
http://www.e90post.com/forums/showthread.php?t=532585
http://www.e90post.com/forums/showth...ht=amp+upgrade
http://www.bilstereoforum.se/showthread.php?t=2356
http://www.e90post.com/forums/showth...hlight=level+3
http://www.e90post.com/forums/showthread.php?t=833581
http://www.m3post.com/forums/showthread.php?t=443043
http://www.diymobileaudio.com/forum/...creations.html

not all of the above are high fi upgrades but the parts in genral except for the cleansweep could be used in any BMW system I think.
Easiest most foolproof upgrade path is a MusicarNW system.(not cheap though)