You don't even need HDMI! The "Standard Dock" which I got with the Costco deal has only a USB port in it, but on the back there is a headphone jack and audio pops out just fine. I tested it already. So the car dock has all the needed connectivity on the phone side, but for some reason they didn't simply put a jack on the back of the car mount. They could have used the same circuitry from the dock! Oh well, please keep up the good hunt for the cable, and please post if you find one. Thanks!