Accessories Is there a USB audio out cable for the vibrant?

Ok, so I've seen this on the OEM Samsung Vibrant dock here:
Galaxy S t959 Desktop Dock | Samsung Mobile

If you look at the third pic, you can see that it has 1 USB connector for the phone, but it has USB and 3.5mm audio out jacks on the back. That must mean that the dock is splitting the micro USB from the phone into USB + audio out.

Does anyone know if there is a separate cable that does this? Or if there's a pinout for this? I only see the standard 4 pins on the USB connector of my phone, so imagine that this may be a chip in the dock itself that splits out the audio.

I'd love to be able to get a cable that splits out the audio too, so that I only need to connect one cable. Also, I'd like to get a car dock that does the same (slide in the phone, one connection, does power & audio) but I don't think that the OEM car dock does this (can't be sure, haven't seen many pics of it).

Anyone have any info on any of this? Thanks!