I also have a support request in with tyan, I'll report back how it goes. I'm expecting a better answer than the equivalent "We do not support uefi boot phases beyond psp post unfortunately"
I went ahead and grabbed an asrock romed8-2t board to replace one of them. Not willing to wait for broken bios updates to address the issues I have with it (mainly the "all or nothing" fan control given that one of these machines sits in a small rack behind me in my home office), and the other tyan board can go in a closet rack.
[re esxi support: I moved to proxmox for homelab stuff and haven't looked back at esxi, given the picky hardware support and generally footgun tendencies of vmware/vsan when you only have a few nodes]
I am running esxi 7 on the same board without issue (although I did not update the bios!) This includes using multiple pcie 4.0 x16 nics which was the main purpose for getting one of these boards. I used several different cpu coolers and do not have any noise issues even when stress testing with proprietary sw. I also have a couple of asrock rack mb and supermicro all with pcie 4.0 support. I like the tyan the best so far although the supermicro is a unique ff (smaller than atx and uatx but slightly longer than a mini itx) that I am using in a custom case.