Well its nice to find more people having the same issues I am. Scott, I am trying to do almost exactly what you are. I replied to another thread you posted in then came over here. As far as the USB DAC working. There is no answer on the web that I can find. I actually posted in the forum of one of the DAC manufactures and they basically said give it a try. That is why I was looking at the bitone.
I have my Thrive in the dash now. Right now I am using the headphone jack on the back of the dock. I am using a 3.5 to RCA (red white cable) and that is going into my head unit. I am planning on using the digital signal of the HDMI out, passing that to the bitone which will go to my HU then out to my Amp. Only problem I see there is that my head unit might degrade the signal. But how else do I handle blue tooth calling? I want the call to come through and the music to drop. Anyway.I am in the same boat.
One thing I can add is that right now I am using an inverter to power the tablet. I know the issues. I think I can wire it to a DC power supply. But I did not get that far yet. Right now my setup is working as far as audio but I can tell a big difference when connecting my iphone to the Alpine which bypasses the iphone dac compared to the Thrive internal DAC to the aux in.
Sorry for the rambling. But maybe we can all come up with the best way to handle this.