Here's the trick to do it (and it's been verified on 3 other Win 7 systems):
1) R click on your speaker icon, select 'Recording Devices' (if you have the sounds dialog up, it's the 2nd tab 'Recording')
2) R click in the white space, be sure that BOTH "show disabled devices" AND "show disconnected devices" are checked.
3) **Now this step is going to take a little bit of thought for each computer being used: on my laptop (HP Elitebook) I get a device "Stereo Mix", ENABLE this device.
4) Click on Properties, go to the tab 'Listen'
5) Check the box "Listen to this device", also change the drop-down box below "Playback through this device" to be your second audio device
-- To verify that you've done this correctly, go back to the Sound dialog tab Playback, you should now see both of your audio devices showing the little green graphs moving.