What audio feature do I get with the NVIDIA PureVideo Decoder?
The NVIDIA PureVideo Decoder supports Dolby Digital 5.1 decoding downmixed into 2-channel stereo, Dolby Pro Logic surround sound, Dolby Digital 5.1, and DTS S/PDIF digital output. If you plug in stereo speakers or headphones into your computer you will hear all of the audio in stereo mode out of two speakers. In order to use surround sound 5.1 speakers you will need to use an external audio decoder and change the NVIDIA PureVideo Decoder audio properties to S/PDIF mode.
How do I turn on S/PDIF mode?
Browse to the NVIDIA PureVideo Decoder Properties and select the “Audio” properties page. Click on the “Speaker Setup” button and select “a receiver” and then check “via an S/PDIF cable”. After this is done, the NVIDIA PureVideo Decoder will be in bypass mode and output all audio to an external receiver or decoder, including Dolby Digital 5.1 and DTS surround sound.
Does this product support Dolby Digital 5.1 surround sound for my 5.1 speaker configuration?
Yes, the Gold and Platinum product SKUs support Dolby Digital 5.1 decoding on your PC. You can also use an external audio decoder and set NVIDIA PureVideo Decoder to S/PDIF mode. All product SKUs support S/PDIF mode. For instructions on configuring S/PDIF mode, please see the "How do I turn on S/PDIF mode?" FAQ.
Does this product support DTS surround sound, my 5.1 speaker configuration?
Yes, the Platinum version of the product supports DTS. You can also enable DTS pass through mode using an external audio decoder and setting NVIDIA PureVideo Decoder to S/PDIF mode For instructions on configuring S/PDIF mode, please see the "How do I turn on S/PDIF mode?"
Taken from the nvidia guide as its easier to understand than my waffling
