Well the Bav Sound stuff is overpriced. The biggest problem with the Hi Fi is the Hi Fi amp is weak, so very weak . And the stock speakers are not that good especially the under seats. Technic has been gone from this site for over a decade. He may still have his website up for harnesses and speaker adapters though . His stuff is not a fully commercial product not home made.
There is no reason to upgrade to L7 it's not necessary to get good sound . Having decent speakers in all position's and upgrading to something like a Helix DSP/amp will be better than an L7 system could ever be. The Bavsound and Bimmertech amps are rebadged Helix Amp/DSP (Also called Audio Tech Fisher which is the website for the there two audio lines Match and Helix )
https://www.audiotec-fischer.de/en/
You better be sure which system you have Hi Fi is a 6 channel amp and Top Hi Fi is 9 channel the wiring system is completely different between the them .
Please Read the Links .
Also Top Hi Fi Logic 7 is a pain to retrofit because of the optical connection between the amp and head unit and the 9 channels and it is not all the great anyway.
Technicpnp.com website is in the following list of links.
Last two links are no longer supported here buy you won't need them with Hi Fi
Please read the 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/attach...1&d=1209780865
http://bmwcoders.com/forum/3-er-8/bm...1-e92-e93-291/
http://technicpnp.com/menuDiagrams/d...e90_92_93.html
http://www.musicarnw.com/page-2/
http://www.e90post.com/forums/attach...3&d=1169133185
http://www.e90post.com/forums/attach...1&d=1209780605
http://www.e90post.com/forums/showthread.php?t=641323
http://www.e90post.com/forums/attach...4&d=1278871872
http://www.e90post.com/forums/showthread.php?t=343673
https://www.bimmerfest.com/threads/e...n-752.1275694/
base system wiring pre/post 3/09
https://www.google.com/url?sa=t&rct=...tDpLJPcGkw_ui_
Base System Guide
http://www.e90post.com/forums/attach...5&d=1493273253