I run a Ga-x99-UD4 board and my board had a update to run 16gb sticks.
Beta BIOS - F13b 8.17 MB 2015/07/03 Asia China America Europe Europe(Russia) : FTP / Http
Support 16GB DDR4 memory module
Improve HDD compatibility
If the updates are not saying that then you can't run 16gb sticks. If you are going to return the memory. I would just get 8 - 8gb sticks of 2133. Yes in theory it says it should run at 3333 but it really still runs at 2133. Plus 2133 vs 3333 you not really see a speed boost.
I am happy as it is right now 64gig of Ram is more than enough, it is just a little disappointing that the xmp does not work for me. I switched from Asus to Gigabyte few years ago as the maximus V was having issues with SLI, after numerous unofficial bios updates at ROG that did not work I gave up and switched to the Gigabyte g1 sniper 5, never had an issue and it was the main factor I invested in the X99 SLI.
I would be interested to find out how the Thunderbolt 3 works when I connect an adapter for thunderbolt 2 devices, as a music producer I want to invest in the new thunderbolt sound cards but something is telling me..... it will all go south on this motherboard, I may be wrong
I already had a problem with Firewire, I tried 3 different PCI cards and although device manager claimed the device was working fine it would not communicate with my external sound card MBOX 3 PRO, did not have this problem on the Sniper motherboard. I think I may have made the wrong investment but a motherboard is simple to switch out if need be...