It does seem xbvr's DLNA serving is the problem. xbvr thinks DeoVR cannot handle the audio format, so it doesn't provide the audio to it.
I have watch so many mp4 with audio. DeoVR is not the problem. DLNA is.
By the way, have you heard about Stash? It's very similar to xbvr, but much more powerful. It used to not serve DeoVR well, but today I just make it possible. Not using DLNA at all.
Now with my special modified Stash, you can browse and preview all your VR scenes, then click on a link to launch the file in VR, just like Skybox does. Quest 2 should be working.
Because it's only possible with my modification, so for now you have to go to my cloned repo for the modified release:
With Stash, you got a personal website that can organize all your performers, studios and scenes. Their community is at:
https://github.com/stashapp/stash . Feel free to ask them questions in discord server. They are nice guys.