hey,
the limited edition and the regular edition are the very same version except for the power supply
if you have very low ohm inears you might benefit from the better power supply, but you can also buy the power supply alone incase you might need it with the regular version
as for your questions, there is no such thing as 7.1 through an optical toslink, your mixamp is converting the 5.1 signal into a fake 7.1 signal
so yes true 5.1 will sound a lot better than the 7.1 you listened to
your audio technica are fine too, stick with them 
Cheers for the response I picked up the standard one as there is a very good sale on atm.
I just got them today but cant get the chat vs game mix very good, what do you use to get the chat audio into the x7? I tried using a thumb usb into the input at the back but it gives me a lot of static with the chat, never had this issue with the old mixamp which I has det up the same with into its mp3 port (as it is the old one that doesnt support usb headset). I have got the ps4 to output the chat via optical now but when people talk it has a mute or fading effect on the game audio which makes the x7s really unuseful in competitve team games..
Thanks for any advice, if you have got it working this way please let me know the model of thumb drive as maybe its just incompatible output? Also I seen a post saying you had a soundwhore profile but couldnt find it, could you point me towards it or how id go about tweaking it myself for a specific game.. Thanks again!
Dave
Edit: bought creatives bluetooth adapter hopefully this helps.. Still dunno what to do about the eq settings though