Well it looks we have a winner!
God knows why (maybe I forgot to sudo grub2-mkconfig -o /boot/grub2/grub.cfg?), but this time adding
... quiet xen-pciback.hide=(00:1b.0)
to GRUB_CMDLINE_LINUX worked, so
$ sudo xl pci-assignable-list
finally produced
0000:00_1b.0
I started sys-audio then and it was up! Still, I was notified with some error messages, yet to discover what they are, and to check if audio actually works.
For now, @zithro I wanted to thank you for supporting me not to give up on Xen PCI passtrough guide, which was crucial, regardless the fact that I used it before you wrote about it. Your message inspired me doing it again and again to check both static and dynamic methods. So, I am indeed happy to flag your first non-self solution at the forum!
If you are interested to investigate further to a fully functional sys-audio, please let me know.
