Well it didn't work for me with the EP45 or my EX58. When the Gigabyte screen comes up you have to click on Delete to get to BIOS. If there is no keyboard response ,how.
I'm not sure why it isn't working for you. I've had no problems with a P35, P35C, EP43, EP45, and P55A mobos. All Gigabyte. In my experience, the USB keyboard is recognized during POST, and I am thus able to enter the BIOS setup, even if Legacy USB support is disabled. I believe that the default is enabled, actually.
Is your keyboard directly connected, or is it through a hub? I've always directly connected my keyboards to the rear panel. Does your keyboard have a built-in hub or other multi-function device? I've always used a pretty basic keyboard. Have you tried a different USB keyboard? Also, try clearing the CMOS and trying again, just to ensure that you're in the factory default state.
Hope that helps, because I'm out of ideas.