Can't you just plug one of these
into the aux jack under the armrest and then set the stereo to aux input?
The car stereo would see the A2DP adapter as just some audio device plugged into the aux port and the A2DP adapter would communicate with your A2DP phone or MP3 player and pass the audio through to the car stereo.
The A2DP streaming audio quality through the aux port should be much better than what you get from an FM transmitter broadcasting to your car radio over FM radio.
I wouldn't get the particular one pictured because I read reviews that said you can't charge it and use it at the same time. If you plug it into a power adapter, the bluetooth is disabled. You would have to keep fiddling with it to charge it when you aren't using it and that would become a hassle really fast.
Does anyone know of something like this (a different brand/model) that can be left under the armrest plugged into the aux port and the under armrest power or USB port to charge and will keep working while it charges? Ideally it would be specifically designed for use in a car, come with a car charger and power off automatically when the power is cut.
Has anyone tested plugging any bluetooth adapter into the aux jack and streaming music and calls from a stereo bluetooth phone?
I'm thinking that getting the new Garmin 765T that has both A2DP audio streaming and bluetooth hansdfree and teaming it with an A2DP adapter would be ideal. It looks like calls, music on the device and the GPS directions would all play over the car stereo speakers wirelessly.
https://my.garmin.com/shop/shop.do?pID=14926