I have no idea why but trying to fix the problem using the sound control panel also causes my guest to hang on occasion or totally lock up forcing a reboot. I've tried two different model USB headsets with the same result in both cases.
Another issue that has developed is the sound output of the guest system is garbled and sounds staccato and choppy, a problem independent of the model of headset or output device. It does so even on speakers.
What is interesting about these issues is that until I upgraded the guest OS to Windows 7 Pro, I never had any such issues. Windows XP played well with VB. Are there some recommended sound settings for Windows 7 Pro? Perhaps my VB settings are incorrect.
I referred to the user manual first, but it offers little in the way of troubleshooting or recommend settings for various versions of Windows.