I can’t really answer that question, sorry. The game is not even officially supported, I never tried it myself.
What I would have suggested is disabling ‘Use built-in audio device’, but apparently you tried that yourself already. That’s the only thing I can imagine to affect your issue. With that option disabled vorpX does not touch audio devices at all.
SteamVR has a similar setting in its option menu (Settings > Audio), might make sense to check that one too.