The head unit in the L7 has a fiber optic output to the L7 amp that uses
a proprietary code . L7 speakers setup has 13 (or 11 ) speakers and 9 channels.
1)You could reprogram the radio for Hi Fi output(something people do to interface with the MS-8) but you loose the graphic equalizer in the head unit and surround sound. I'm not sure that there is a prewired analog output from the Head Unit to the amp area? Does anybody know?
2)You could buy a mobridge preamp to feed the new amp or amps and retain the Logic 7 in the Head Unit.(as it is the only device that will translate the fib optic signals from the head unit) Then you still need away to figure out to do with all the speakers with only 6 channels to replace the 9 in the original L7.
There is a block diagram of how the L7 is connected in the following links.
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.bawarec.ru/manuals/3er/e9...3er-e90-12.pdf
http://www.musicarnw.com/page-2/
http://www.e90post.com/forums/attach...4&d=1278871872