So it’s connected to the Mac running Roon core via USB? Just to be sure you have checked in settings/audio ? It should show up as connected to the core like image below. Mined been renamed tj Dining Room but it’s an RME ADI 2. Enable it from there and it will show up.in Zones. If you have done this already and it’s not showing up.in audio settings. Check cables are connected and the Mac is seeing the DAC in its audio settings.
Maybe Audirvana had locked the DAC in exclusive mode making it inaccessible by Roon. And if so released this lock somewhere in your troubleshooting process making the DAC available to Roon again.
Something to consider next time you run into this.