Hi JohnC,
you have to get access to the console and check the alsamixer settings.
alsamixer
Select your DAC (F6) and then check each setting available.
Frank
- Get access to the console:
Use SSH from your PC
- If you are not familiar with SSH read this for Windows or this for Linux/MacOS
The default login for RuneAudio is "root" with the password "rune" (without quotes).