We rented a car when we were in Virginia and we managed to get a Toyota Prius. The radio was playing and I hate radio as much as I hate TV! I had my music on my iPhone but I didn't have a car adapter. But hey, the car supports Bluetooth audio. I poked around in the menus but I couldn't figure out how to connect. I pulled out the owners manual but there was no mention of audio? I found there was a whole separate manual for the audio system!
It was a little hard to follow the manual because it described multiple versions of the audio system, none of which seemed to match our vehicle. I figured it had to be possible since a bunch of iPhones were listed on the Bluetooth menu. It turned out that might have been part of the problem since the manual said you could link up to five devices, and there were already five. No problem, I'll just delete one. Except the options to delete that were described in the manual didn't appear on our car. I wonder if rental cars are locked down somehow so you can't mess with certain settings?
I gave up at this point. But then I remembered seeing something about USB in the manual, and I did have a USB cable (from the charger). Sure enough there was a place to plug in a USB cable and when I did my iPhone showed up and played perfectly.
The moral of the story is - don't get so wrapped up in the wonderful complexities of one approach that you forget that there might be other (simpler) solutions.