Just to update here
In the end I have gone for Gigabyte Aorus Master for these reasons
- Has IOMMU/ACS/ARI BIOS options.
It looks like MSI has these setting on the Threadripper motherboard though. https://youtu.be/37RP9I3_TBo?t=756 - Beta BIOS availability and more vibrant community for sharing beta BIOSes.
https://forums.tweaktown.com/gigabyte/28441-gigabyte-beta-bios.html
https://forum.gigabyte.us/thread/7098/x570-beta-bios-thread - The audio problem has been fixed and I will be using digital output anyway.
https://forum.level1techs.com/t/x570-aorus-master-audio-issue-with-linux/148784
Outstanding problem