Hello webdove, you can try to read on overclock.net there was a big disscusion about that.
Anyway I am able to set this settings and I don´t now if there is some combination of settings which can allow you to set these settings... Seems that you tried everything.
I can can send you my LCD settings... Meanwhile check this info about firmware... ->
https://www.asus.com/support/FAQ/1036750/ Hope we can find solution... coz there was some older FW´s...