Temporary work-around for people who can't use K90 in BIOS, but who also own an M90
I found an easy way to access and navigate the BIOS using only the M90 because the most recent update to the K90 has stopped it from working on what mainly seems to be ASUS boards during POST.
Firstly set your M90 to Hardware Playback mode, then set up a new profile. Add macros for the keys that you would normally use to access or navigate the BIOS to the different macro buttons (Del, Up, Down, Left, Right, Enter, Esc, F-keys, etc.). Save the profile to the M90 and set it as the active profile then reboot. You should now be able to use the M90 during POST as your keyboard rather than switching keyboards to access the BIOS (it's even better if you've got a UEFI BIOS because you only really need the button to get into the BIOS and you can use your mouse from there).