Some RAM brands should make it to 2133mhz. And heck, if you configure it manually (timings included) you should be able to get there.
I think your best bet is Corsair Vengeance RAM.
yes you can overclock the ram manualy thats no problem, but you will be absolutly fine with 1866mhz ram. i dont see the bennefit of buying much more expensive 2133mhz or even 2400 mhz ram, i would personaly prefer 1866mhz with low cas latancy.
I know the software suite is still a pile of steaming crap except the wifi go program . I really prefer bios .
I say that and it just gave me a auto tune of 4552.2 at 1.413 volts :)
I run 32gb's of 2133 mhz ram in mine with no problem
I had to alter the timing manualy slightly though and that was it.
It'll support it but i think your system will downclock it to 1866mhz.
I am pretty sure just flip it to manual and set it to 2133.
11,12,11,33 at 1.6v
supposed to be 32 but wasnt stable unless I upped the voltage to 1.65 (which i wasnt happy with)
I was going to up mine to 16g once i started crossfiring. So maybe no issue ? Running 8 gigs of gskills with 10 12 12 31