I didn't quite understand what to do.
I delete the VEGA driver with the DDU, afterwards I leave 1 or more cards connected?
which bios exactly do you mean, the final version or the beta?
I got the board yesterday and can't get more than one to work. Have also tried the latest BIOS and Beta BIOS with 4G decoding etc. but nothing works.
I also made your IOMMU settings, even without success.
Please ask for help:)
Use DDU to unistall the Vega drivers. Leave them installed in the motherboard. Then try reinstalling.
I actually prefer the next to last BIOS. There are issues with the latest X350 Gaming Carbon Pro/X350 Gaming Pro bios.