I'm curios here too. My 2005 4.8is has had mixed results with factory bluetooth. At first it would not pair with iPhone 5s so I pulled fuses. Then it worked with mixed quantity for a few days. Then it shifted to only having audio from one front speaker. Pulled fuses again and it worked for an hour.

Last week I bought a soundicity 3 which is the same as the audiovox media bridge. It's my effort to replace the factory blue tooth. It sounds a bunch better but still not great for phone calls. The BT audio music from phone is great. It also added satellite radio which has good sound quantity but channel tuning is a bit tedious. Overall the media bridge is pretty good. Main issue I am having is sound level balance between the inputs (satellite input is much louder than BT).

I see the factory BT unit had two antenna ports, wonder which is which? I've also been wondering if newer BT module might work better.

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2003 E39 530i
1992 MX5
2005 E53 x5 4.8is (sold)
1990 K75S (sold)