To me, it sound like your hardware have a shitty iommu handling, and afaik, there is no solution to that (maybe you could have luck by upgrading your bios). You can also try the “no-strict-reset” flag.
And the alternative would be to keep sys-audio for everything that work on your computer, and set the audiovm of sys-audio to be dom0 so dom0 could handle the things that you hardware cannot handle in sys-audio.
(You could also try the same technique used for GPU passthrough (the PCI hiding part in “GRUB modification” Create a Gaming HVM) )