I also have the 1950x and x399 Taichi, with two LSI 9211-8i with latest IT mode FW. The latest BIOS causes one of the adapters to not be detected in my build, but I'm sure it is unrelated to unRAID since it also fails to complete POST intermittently with the second adapter installed.
I have all VM related features enabled in BIOS along with global c-states with no issues though, currently up 5 days after the bios experiment.
One strange issue I just can't tackle though is running an Ubuntu VM. I have pfSense (BSD) and Windows 10 VMs up fine, but as soon as I try going though the install process with Ubuntu the entire unRAID server becomes unresponsive, and I am unable to retrieve logs.