Just as a point of information, I have successfully played music using bluetooth A2DP to my Pioneer DEH-P7000BT in-dash stereo.

Occasionally there are some dropouts, but it wasn't too bad. I haven't tried it since the latest firmware update.

In my case, you pair the phone with the stereo and it pairs each of the different profiles (including A2DP). Then to play music I select "Bluetooth" as the source for audio (on the stereo) and then play something from the phone.