SOLVED:
After forcing the Omen to boot from a USB2 thumb drive from the F9 boot menu, it now boots from that thumb drive successfully, without having to go back to the F9 or F10 boot menus. This worked for the 3 different USB2 thumb drives. YES!!! (Is this some sort of security feature?)
And if that was not good enough news already, I burned the latest Linux Mint version to my oldest, slowest USB2 thumb drive and not only did it boot fine, and recognize other USB2 thumb drives when plugged in, sound and video work properly. (Such was not the case with Linux Mint 17 Debian Edition.)
I'm going to LOVE this laptop ...
!~}>