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.
I would suggest something like this if you were on a budget I'd keep in mind though that creative isn't that great with drivers and has a history of having buggy drivers.
asus
http://www.newegg.com/Product/Product.aspx?Item=N82E16829132007&Tpk=Xonar%20D1
creative
http://www.newegg.com/Product/Product.aspx?Item=N82E16829102041
and this if you were not
Expensive high end
HT OMEGA CLARO HALO
http://www.newegg.com/Product/Product.aspx?Item=N82E16829271004
You can use the higher end Asus Essence cards as well but they give you an adapter to use S/PDIF
Intel Core i5 2500k
Asrock Z68 EXTREME4 Gen 3
Gigabyte GeForce GTX 670 2GB OC
Corsair Vengeance DDR3 1600 8GB (2x4)
Creative Soundblaster X-Fi Titanium Fatality Professional
Samsung 830 256GB SATA III SSD
Seagate Barracuda 500 GB SATA II
LG 12x Super Multi Blue WH12LS38
CM Storm Sniper
Corsair AX850 PSU
Corsair Hydro H100
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