I'm assuming that ASUS AURA has steadily improved since its introduction (circa 2014) and that it keeps being improved on new ASUS products. Each new iteration is incrementally better than before in some way.
So I'm guessing that MAXIMUS IX motherboard - omg, a whole year "old" now! - just lacks some of the refinements built into newer ASUS hardware/software?
I know this thread is rather old but I was racking my head trying to figure this out as well. Like OP our software looked identical and I could not get my RGBs to white either. Finally i figured it out. You have to slide the saturation slider all the way down.
Figured I'd post the info here in case anyone was wanting to accomplish the same.