Martin_167 :
I had the same problem with 7.1 the solution was to properties of the headphone, unplug it and uninstall the drivers not LGS the drivers adn it worked again
This is the correct answer and I've been Googling and trying different things for two hours. I'll reword it a little though:
1. Install the latest version of Logitech Gaming Software.
2. Go to Control Panel > Device Manager > Sound, Video, and Game Controllers
3. Right click your Logitech Device (for example mine was: "Logitech G633 Gaming Headset")
4. With the right-click options showing, unplug your USB headset.
5. Click uninstall device (if there are options to uninstall the driver as well make sure to check the option on before uninstall).
6. Plug your USB headset back into the USB socket.
7. Test the surround sound option in Logitech Gaming Software