All the tests above were done from a HTC Titan with Windows Phone 7.5 . I will indeed try with the S3 at some point.
But again, today I've been driving for 2hrs, and music via BT sounded really good, which keeps surprising me. I have no clue what the Titan+MKi9200 are doing - and possibly I will never know, and in addition to that I am feeding my Alpine via Aux. Level is lower than when playing the iPod via the Alpine, but other than that, it's just good! I would not even be able to tell which of the two sources is better, in all honesty. I'd expect a much lower quality from BT sources, all considered. Maybe my stereo setup needs more tuning. It's getting old, after all...