The computer does not need to provide a 5 channel source to the adapter for the Plantronics implementation to operate. All the work is done on the Dolby powered USB adapter provided in the package.
The adapter implements a combination of Dolby technologies by using Dolby Pro Logic II in conjunction with Dolby Headphone. Pro Logic II takes the 2 channel information from the USB output on the computer and creates a very accurate estimation of 5 channels. It then hands that off to Dolby Headphone. Dolby Headphone then uses that information to create a surround sound experience on the 2 channel headset.
This implementation was developed directly with Dolby and the experience is very accurate.