I found my settings as described, I'm on EE and this post was useful, thanks.
I have a Bluetooth Mirror which clips over my exisiting rear view mirror.
I had a play with it and basically when I get in to my car, I turn on my Bluetooth Mirror and Car mode is activated which is great, it plays the voice through my car stereo (my mirror connects to my car stereo vi a FM channel). The only thing I cannot seem to get to work is playing music, it plays the music through the phone and not through my bluetooth mirror and subsequently my stereo. The weird thing is the S5 voice commands and the phpne calls etc do play through my stereo.
Is there a setting I missed?