I've tried looking that up as well to see if you would get the surround sound through the optical cable with the Asus premium boards. Normally that is something that would be simulated by dolby digital live or the encoder as it will be labeled as. I use a astro a40 myself. And astro suggests for the surround sound to get a card with dolby digital live, and quite possibly dolby headphone if it has it. Also something they do not provide as well is the usb chat cable that goes from your mixamp to your computer to enable pc chat.
I honestly feel you may need a sound c rd to achieve what astro has in place. I'll list what I have but I will give my suggestions and the suggestions I have received through astro's forums.
Again I have the wireless 5.8 ghz mixamp and Astro A40.
You can use the higher end Asus Essence cards as well but they give you an adapter to use S/PDIF
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