Are you sure that your car's head unit wasn't playing the music files? That would explain why pandora would not work but MP3 files did. If that's what was happening, you weren't getting audio out via the USB, your car's stereo was using the USB connection to read files off the SD card and play them.
+1. That is exactly what I was going to post. The USB standard is NOT an audio standard. There is no analog Audio passed through ANY USB port. There is only power and data. You theoretically could have audio converted to data and sent over the USB cable to be interpreted by a device but that would require a special setup. As VegasJay said, if you plug the USB into a standard head unit it is only using the EVO as a USB drive to play the MP3's from it.
You also could have the audio sent through the HDMI cable as that has audio on it. The main problem is it is digital and not analog. So again you need a unit to convert this to analog to play through your head unit.
I would also like a nice way to send BT audio to my head unit.
So the easiest way is to send the audio out via Bluetooth to a receiver that outputs to the standard headphone 3.5mm (1/8”) plug that could then be input on your HU's AUX port.
Make sure you get a BT Receiver and not transmitter. i
i
This is the one I am looking at. I am still looking around for the best one.
http://www.amazon.com/Miccus-BBMR-0...tag=hawk-future-20&ascsubtag=UUacUvbUpU169253
Edit: Okay I think this may be the one for me as it has power and a remote. I think would be work GREAT with the Evo.
http://www.amazon.com/Kensington-Li...tag=hawk-future-20&ascsubtag=UUacUvbUpU169253
Now I have a question. I already have BT on my had unit for phone calls. I wonder if I can stil use my main HU for calls but this adapter for the audio. Can I pair and use two different BT devices with the Evo at the same time like that? One for phone calls and the other for audio!