Hello BruceTHolmes,
Welcome to Apple Support Communities!
We understand that you're using a USB sound card for your input speaker source and using your AirPods as the output source but you're unable to hear input from the USB sound card through your AirPods. We're happy to help out!
Check out the article below for help with not hearing sound from your speakers.
If you can’t hear sound from your Mac speakers
The next two articles we'll provide you with are going to be about Input and output speaker settings for the Mac. Go through these articles and ensure you have your input and output set up the way you want it to be.
Change the sound output settings on Mac
Change the sound input settings on Mac
Also, check out this article as well for it speaks to using earphones:
If your Mac switches to a different audio device
Let us know if that worked for you.
Thank you for using Apple Support Communities.
Take care!