Thanks for sharing your report with us, @Patrick_O_Brien!
So we can better assist you, please provide a brief description of your current setup using this link as a guide.
Make sure to describe your network configuration/topology, including any networking hardware currently in use, so we can have a clear understanding of how your devices are communicating.
Was Roon previously able to see this DAC? Are other endpoints seen?
Have you tried rebooting the DAC and your Core machine?
Thanks,
Dylan