Hello panworks,

Noel gives some great advice here, often times Windows is finicky about letting you use "what you hear" or "stereo mix" options as Windows themselves stopped supporting those features (apparently due to potential copyright issues).

You mentioned you tried all the usual stuff including audio drivers, did you try completely uninstalling the driver for that sound card and rebooting your machine? That will force Windows to download the newest driver for that device and reinstall it cleanly.