I've just bought a Kenwood head unit for the same reason for Bluetooth audio, it works well and sound is very good, i have a Desire HD so it does work. I've been playing music from music, spotify and poweramp apps, can control on head unit but the track titles etc. don't display.
Have you checked settings such as media volume and bluetooth options, might be somewhere on there for enabling audio.
I did pair with my android tablet but no audio from that, hadn't looked further into it though.