That is one impressive motherboard, from looking at the specs.
Quick question: what BIOS version is currently on the motherboard? I believe from your initial post that you hadn't done anything with updating BIOS, if I recall correctly, and I just wanted to take a look at the various versions they released.
What a bizarre error condition, to have 2nd boots seemingly OK - that's a new one on me.
Forgive me for being behind the 8-ball on your issues - I AM trying to get up to speed on the thread, and will do my best to help you, if I can. :)
I did double-check the supported memory, and all seems fine and good with that (I was also pretty sure you would have checked that too, but I was just trying to be thorough).
Also, early in the thread, you indicated all maintenance and firmware being done. For the maintenance, are you strictly referring to Windows maintenance, or driver maintenance, or both? Thanks for some clarification on that, too.
I ask, because for one of the computers I built, there were some 3rd-party drivers for the USB 3 support, and it made me wonder if you had applied the base drivers from the disc that came with the motherboard, and then was wondering about any subsequent application of drivers from the Gigabyte site.
Bob Bone