The factory retrofit is expensive and convoluted. (See above)
also I don't think the audio is as good.
Yes a2dp is streaming bluetooth music.
If you just want Ipod I think BMW does it for around a grand at the local dealerships. I think they will tell you usb isn't possible on some of the older models even though it is . What you want is in the threads try doing a search for USB and 6fl.