BigBehr.  I have had the issue you describe (working streaming audio, then stops) occasionally, but I can resolve it by pausing the phone audio, toggling the inputs on my car stereo, then hitting play on the phone again.  I had a HTC G2 previously and it worked flawlessly with my 2012 Subaru standard CD player with mp3/usb/bluetooth.

However, my larger issue is that the DROID DNA will not auto-connect to my car bluetooth.  I have to manually connect it every time I want to use it (Phone, Settings, Bluetooth, Click my car under paired devices).

I absolutely love everything else about this phone, but this blue tooth issue is driving me crazy.  Any suggestions out there?