You did try to explicitly re-select and re-save the selection.
Yes, each time. I have also tried restarting the computer with Digirig attached.
What if you select computer’s internal audio components there instead of Digirig’s?
When I select the system sound devices, i get the same error message.
Sounds (pun?) like the issue is with app or with the system software. Let’s continue dividing and conquering: are you able to get audio configured with a different app? E.g. Vara, FlDigi or JS8Call?