What are you trying to do?

What are you trying to do exactly? The boot from a USB device didn't really become all that useful until Microsoft made it an option for installing Windows 7. Before that, it'd just be the Linux users who probably take issue with my earlier comment.

Also UEFI is essentially a BIOS replacement that is being phased in, and Microsoft is pushing in a big way with Windows 8.

Finally, having had similar issues, I'd suggest you contact Benson Jiang (think that's how you spell it): cl-benson at asus.com . He's helped me a few times when I had some questions about Asus motherboards. Not like you have a lot to lose if it doesn't work out given you are kind of stuck as it is.