If you find the screen in the shot below in your Control Panel, under Sounds and Audio Devices, click the ringed 'Advanced' button, you'll find the speaker settings, which you can change from 'Desktop Stereo', to '7.1 Surround', and virtually every configuration in between. I was just wondering if you set it to the set up you require, in this case, 6.1, it might default back to it when you remove the headset.