Ok- I may have found a workaround. I disable the monitor audio in two places. One is in the Device Manager. But it keeps showing up, right?
So I disabled it also in Windows. There's an option to tell windows "don't use this device"- it seems to be separate from the Device Manager setting. Let me see if I can find it...
Ok, in W10, it's "Manage Sound Devices"
This worked to finally get windows to stop thinking the USB Hub built into my monitor was a preferred audio output device.