If you can't set up a 5.1 configuration, go to Start > Control Panel > Hardware and Sound > Sound > Playback > Configure > 5.1 Surround. Save and accept the configuration then start the Rapture3D application and make the proper adjusts. However, this is rather unusual because if you're using a soundcard with Rapture3D support, you should be able to configure the speak setup from within the application.