While I still wonder what the issue is, I have found that Bluetooth audio is a nice workaround, as documented here:
I would like to respond to this comment below:
I do not think that developers owe me or anyone an explanation on this issue. I share your desire to know the cause, but it is not their responsibility to identify it.
As I mentioned in the linked comment above, I think that the cause lies with the hardware itself. Hopefully someone from Purism can identify the cause of the issue someday, but since sys-audio is still a relatively new part of Qubes OS and is optional, I do not expect much investigation to be had anytime soon. I also think that I am probably the only person experiencing this issue, and it is not very important to me. I am very happy with my Qubes OS setup as it is.
I greatly appreciate the work being done by the developers of Qubes OS and other free software projects, and I think we need to remember that we are the beneficiaries of their free labor.