For anyone else in the future - I figured this out by accident: I was using a third party tool (Voicemeter) to route audio on my PC and I had the Pimax speakers set as one of the outputs there. That seemed to be causing some issues with the DeoVR playback engine. As soon as I just set the entire Windows sound output to exclusively the Pimax speakers, the problem went away. Perhaps whatever video playback engine DeoVR uses REALLY wants complete control of the audio output and freaks out if the audio is being routed in another route.
Incidentally this also solved a similar playback issue I was having with the Playa app where it would constantly say I didn't have HEVC video extensions installed despite definitely having them installed.
Hope this helps someone!
