Success! In the BIOS of my Asus Sabertooth z87, I set both "USB Legacy Support" & "Intel xHCI mode" to "Auto" and disabled "EHCI Hand-off" and now my computer boots normally with my RGB K95 and the keyboard no longer gets locked out before Windows is loaded. You also might want to disable "Fast Boot" though it appears that the "EHCI Hand-off" was the culprit all along on my system. Here's a BIOS screen capture of my now working config:161029145238.BMP