Windows 7, realtek optical audio, evga motherboard problem

I have decided to use optical cable for my audio from the nForce 780i SLI FTW motherboard onto my logitech speakers Z-5500 Digital set.
The problem I have is that nowhere in the config, under the Realtek or Windows, does it allow me to select Optical output, it only points to Digital Coax output, but the motherboard does not have that.

At this point, using the regular cables (green, black, orange) I can get the sound, but I would love to enjoy DTS coming out of the BluRay movies I watch on my PC.

Any suggestions will be welcome kindly

Thank you

Ps I am using Windows 7 Ultimate, and the drivers are working, I do get sound out of the 3 cables.

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