Motorola Droid :: USB Audio Output

I'm toying with the idea of making a car dock for my Droid. The official Droid dock doesn't work with any cases and if the iPhone is any indication, no one will ever make one that does. Plus, it doesn't do everything I want.

I want to plug my phone in with as little fuss as possible, have it charge, output audio to my car stereo through USB. Charging is absolutely necessary, and I want to avoid using the headphone jack for audio if I can because it's an extra thing I'd have to plug in rather than just sliding the phone right in the dock. Better yet if the USB audio output is a constant volume intended for control on another device.

So.. Is it possible? If I need hack a car charger in to a usb audio cable I'm fine with that (unless I could get both in one). This thing would do it, but it looks like it has more pins than standard usb (can't really tell in that pic, but maybe someone knows?), and the Droid doesn't.

My other options are connecting the Droid directly to the head unit via USB and mounting it as a mass storage device, but I prefer the way the Droid handles music better than the head unit, and mounting the USB is an extra step I'd probably get too lazy for. And finally, I'd considered making an app that spoofs an iPod, since my HU has iPod controls, but that's more work than it's worth when the Android music player's controls are just as good.