The USB sound device is called EzCAP USB Audio Capture.

However...
I think I found a workaround. If I leave Realband set to Microsoft Sound Mapper, and start it BEFORE I plug in the USB capture device, then set the USB device as the default using Windows, then I can record sound consistently from it.

Keeping in mind that Audacity doesn't have this lockup problem if the device is already plugged in, I'd say there was a problem with the way realband (and PTW) are interacting with Windows 7 sound, specifically when initialising the interfaces.