I've been running this setup for a few days and the verdict is in:
It sounds EPIC. Very, VERY good. I listen to everything from Dubstep to hard rock to Musicals, and it handles them all very, very well.
I've only had 3 relatively minor problems:
1. About 95% of the time I have to manually go to Settings-->General-->Bluetooth and re-establish the connection with the car every time I get in the car. Anyone know if there's a solution to prevent this?
2. When answering a call via the steering wheel button it auto-selects the BMW's bluetooth. But when making a call via the phone it auto-selects the Samsung unit, and you have to manually select the BMW unit.
3. Volume won't go above medium-loud. It's not quiet, but in some songs it won't get particularly loud, even when the volume on the phone and Samsung unit are maxed. Not a big deal.
Overall it's infinitely better than any other solution I've tried. Highly recommend it if you don't mind having to manually connect it in settings whenever you enter the car.