Nari Ultimate - THX no sound

Having an issue with my THX producing no sound, all of a sudden. Headset 'game' and 'chat' work fine, but if THX is selected as the default device, no sound comes through the headphones. I have tried reinstalling Synapse a few times, as well as a few other 'fixes' found on the forum, such as running windows audio troubleshooting etc, with no luck. Don't really understand why it has stopped working all of a sudden, literally overnight, when nothing has changed on my system....no windows updates or anything like that. Any suggestions to get this working that I might have missed? It's as if synapse has stopped recognising my Nari Ultimates as THX capable...