I am sorry you are having such trouble. The link posted gives exactly what packages need to be installed, and running, as well as the permissions needed (including the 50-sys-audio policy file). Following that I have consistently gotten a sys-audio qube (minus the IOMMU issues with my dell hardware which is unrelated). Though I have not tried in 4.R3 yet. With that IOMMU issue (forum post here) sys-audio will not see my HDA audio device until I restart all my qubes, and then it may work randomly (thought it always sees my audio out for my HDMI connection). I don’t blame Qubes for that one, I blame Dell since its their handling.
Do you notice anything weird in any logs when this happens?