I bought a demo model too, on E-Bay. Also have a full working one on the way. Right now, I'm trying to see if I can flash the demo using the directions from this link http://www.mediafire.com/view/?d4mqgzr4cbrttzu
which details how to un-brick a Kindle.
However, doc was written for a Kindle Touch (which I also have, and it works for it) not a DX-G. I am hoping that I can apply most of the doc to the DX-G as long as I find and use the correct firmware files, but I'm having some problems getting it to be recognized by mfgtool.exe.
Currently, I am looking through other threads here for a solution, but if anyone knows of a document that is written for firmware updates for a DX-G, I would be very greatful.