I received my board yesterday and am now having the "exciting" challenge of updating its BIOS.
I tried using PXE-UEFI from here: https://wiki.ubuntu.com/UEFI/PXE-netboot-install
and got grub starting up, then I got a bit over eager and tried to boot DOS so I could try running the Gigabyte flash program.. before even getting that far, it reset and reported it was restoring the BIOS. Hmm.
There are a bunch of TLAs that are not explained, for example "CSM" is Compability Support Module Configuration... and is where you get to turn off UEFI and set legacy modes. If you turn off UEFI by switching to legacy, you need to reset and re-enter the BIOS settings before other menus change.
Once you've done this it seems to be possible to boot off a plain USB thumb drive, but no sign of legacy PXE function
Then I created a freedos USB drive, I'd downloaded the 256MB image which should be more than enough, right, to hold the Gigabyte bios image and flasher. Sadly, it crashes and resets the motherboard when I try and boot the full freeDOS. I did manage to boot the minimal "fdodin" image, but that's too tiny to be useful.
--- next attempt ---
OK, so I thought "aha, iPXE". I created an iPXE image for USB - very easy in fact, and copied over a usb flash drive, and voila, iPXE started and talked to my PXE server.
Unfortunately, there was a brief flash as the pxelinux.cfg/default menu appeared and then it crashed and reset.
Wow, this motherboard's F1 BIOS version really is a bag of ****.