@evc69 - Hey, welcome to the site! 
This board/BIOS is too old for Bifrucation, only Asus could add or adjust that. There may be some slot that is bifurcated by default, but I doubt it. Test all slots one by one with two NVME in the Hyper card, including the main PCIE x16 slot you’d normally use GFX card in
Also, see here, my comments and testing with Hyper V2 card - [REQUEST] Bifurcation Asus x99-a II - 5820k (2)