Apparently this software takes over and works independently of the PC's sound card. If its not working correctly there is either a problem with the program or some configuration error.
The Playback section, where you would set the program as the default playback device is found at Start/Control Panel/Hardware and Sound and finally the Sound Panel. If its not displayed, RIGHT click in an empty area in the panel and click the two options for display disabled and disconnected devices. If it shows up you can then select it as the default playback device. If it is still not showing up, there is an installation problem with the program (try reinstalling it).
If it shows up and you are able to select it, to go back to the regular PC playback device "Speakers" just manually select what you want in this same panel.
If it still is not working, best to contact the software vendor for additonal assistance.