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However, I have encountered a problem. After updating to the F6 BIOS, Sierra and High Sierra still boots, but the USB keyboard and mouse, which are attached to the USB2 ports at the back, seem to be disabled. Tried unplugging and plugging them but no luck. I check the BIOS settings to make sure they are the same as when I use the F5 BIOS, and they are, but I just can't use the keyboard and mouse. No idea what the F6 BIOS changed to cause this problem.
For now, I am back to the F5 BIOS where the USB keyboard and mouse work properly with both Sierra and High Sierra.
I suppose you have not tried to run High Sierra 10.13.6 (or Sierra 10.12.6) using this board? Can any of the resources available in your guide be used with Sierra or High Sierra?