Help to Ensure [7.1/Surround for Gaming] Working for Headphones

[hatman5700]

Hi, I wanted to confirm my setup was correctly setup for 7.1 surround on my speaker headphones based on the following:
-Sennheiser HD 598
-Astro Mixamp 2014 Edition
-My PC with Mobo-Onboard Optical Port
I have my HD 598 headphones plugged into the mixamp. Mixamp is plugged into the PC via optical TOSlink cable (into mobo port for Optical). Note that it is also plugged in with a USB Cable for Power to the PC. I have selected Digital Audio (S/PDIF) in Win10 for the default sound (not the 'Speakers' option that is available from the USB connection, if I am understand this correctly)
Now couple of questions:
-How can I test for 7.1 surround? The mixamp is supposed to provide virtual 7.1 after receiving digital signal from computer and ultimately produce 7.1 for my HD 598s. I can't test via youtube because no videos properly output surround from youtube. Is there a go-to testing file/site?
-Is there anything wrong in my configuration? I thought I read something about needing a certain signal/encoding format sent from my computer to the mixamp in order for it to do it's 7.1 processing correctly to the headphones, an I'm unsure if my onboard audio from the MOBO is outputting the correct type of Dolby signal or w/e is required? (Does this mean I need a soundcard in addition to the mixamp?)
Thanks

 

[BringerOfTea]

real good stereo is preffered to an emulater 7.1 config. So a decent soundcard and a pair of decent headphones will give you a better experience. The sennheisers you got should be more than enough.