Well I just performed the same modification. I only modifed the power connection and not the audio cables. I still have the power problem occasionally but not nearly as often. The sound seems to cut out occasionally.

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2011 550xi Carbon Black/Oyster, M-Sport, Premium Package, Technology Package, Electronic Damper Control, Dynamic Drive, Comfort Access, Active Seats, Surround Cameras

2013 X5 5.0 Space Grey/Black, M-Sport, Premium Package, Technology Package, Comfort Access, Surround Cameras