Gigabyte 970A-UD3P S/pdif problems

[Janus]

Hi guys,
first of all forgive my english. My name is Antonio and I'm from Italy and...I have a question for you. I've just finished to assebly my news pc some days ago but still can't get ahead with an audio problem. Basically I connect my pc to a Sony Str-db780 stereo amplifier via optical input, but I can't hear anything. I've tried the optical in on the amplifier by connecting a cd player and it works so I think there must be somethin wrong with drivers?
Here it is my system specs:

M/B: Gigabyte 970A-UD3P
CPU: AMD FX-8320
SO: Windows 8.1 64bit

I do appreciate some help, thanx in advance for your time

P.S
I used to have another system based on a amd cpu and a gigabyte motherboard (can't remember the model right now) with optical output and it worked...

[dmdilks]

Just asking if you have it set in the audio control panel to S/pdi ?

Do you have the latest driver from the Gigabyte site too ?

http://www.gigabyte.com/products/product-page.aspx?pid=4717#driver

If you connect speakers do they work ?

Does the little speaker down in the right side task bar have a X in it ?