The guy in that video had a bad Sat module when he fixed the no sound problem
sound came alive because the most loop was completed. The most loop could be complete but the output of the amp bad. If you had a spare amp that you
knew worked I would swap that in . Since you don't I would call he logic 7
amp repair guy to see if the can give better guidance .
http://www.bmwlogicseven.com/?p=3837