Neil,
Thanks for chiming in, I'm a huge admirer of your hacks!
The thin mITX GIGABYTE board I mentioned, from what I can tell, has the same DC-DC plug like the Intel variant. GIGABYTE is just giving you some flexibility with internal components as well. One of my main goals of this project is to have an internal PSU. Inline bricks aren't my style but I don't know how to utilize the pin-outs on the board.
As for my ASRock board, I'm loving it. I'm using it currently on Win7 with my 7870 Tahiti and it zips right along! (Bluetooth on Windows is still a huge struggle!)
I'm kind of putting the cube on the back burner for now. I'm thinking I'll go with some sort of QM87 or HM87 for the BGA processor for higher end integrated graphics.
In the meantime.. I have two Yosemites and a MDD that I'm going to start looking at. They may be stepping stones to my cube project.