Without knowing if testing was actually done with binaural sound that can leave results rather vague.
Binaural sound has specific and lot harder requirements than any stereo music and even notably higher price doesn't necessary mean better for gaming.
Actually music can even benefit from smaller sound stage.
Like famous for music Sennheiser HD650 with likely Dolby Headphone in Mad Lust Envy's guide:
Soundstage:
The front/back depth isn't great. Let's get that out of the way. The width is good, but not close to being the best. The DT990 destroys the HD650 in both depth and width. So how's the air within the soundstage? Well, the problem with the HD650, is that it's a very full sounding headphone. Thick, warm tone tends to make the soundstage seems less airy and smaller.
Positioning:
Positioning and soundstage tend to go hand in hand, so if the soundstage isn't great, the positional cues will suffer. How did the HD650 fare positional-wise? Well, they were good. Not great, and could obviously be better...
Clarity:
You need clarity for soundwhoring in competitive gaming...
I've heard better overall (even the 990's are better for soundwhoring). The problem is that the HD650 is a very thick sounding headphone. Basically, the issues I explained in the soundstage section is what hurts clarity for gaming purposes.
Same things which give it its intimate "front row" musicality hurts gaming badly.
So better to focus to known headphones.
First minute of this is excellent quick test for sound stage with gun shots from different directions and distances:
This was another I used in comparison:
https://www.youtube.com/watch?v=B8xZp0WPwxs
You can easily test any headphones you have with those.
There should be literal feel of space with sounds coming clearly from different distances...
Instead of everything coming from next to ear/in front of face with some sounds just being more muffled than others. (like in cheap closed design garbages)
AKG K702 is pretty much aural "god mode/wall hack".
That ALC1220 is definitely capable to meeting human ear's accuracy when clearly lower ALC889 (at level of budget sound cards) is pretty much there.
http://www.tomshardware.com/reviews/high-end-pc-audio,3733-19.html
Realtek chips just lack proper binaural simulation and only some Gigabyte and MSI motherboards have bundled Creative's software set.
And hence would be stuck with what sound options games have (most games don't even have own sound settings) or Windows 10's Windows Sonic for Headphones which seems average.
Plain 2.0/stereo speaker mix is this sucky:
https://youtu.be/d1_20T8x_OI?t=12m56s
Though technical capability for driving headphones would be likely good enough even if MSI's marketing took little "artistic freedom".
With binaural-simulation from sound card game needs to only output standard 5.1/surround sound.
That Xonar DX is again weird card when Asus bundled Dolby Headphone (mediocre bass bloater) with it while 100 ohm output impedance makes it not so good for headphones.
While 250 ohm Beyers would be fine usual lowish ohm headphones would have rather bad (electric) damping factor.
And for some reason Asus seem to have that same lame output impedance in Strix Raid Pro and possibly Strix Soar.
While once again music might not care that hard, but for games you want good signal control of driver.
At the same time Creative has upped their game with Sound BlasterX AE-5 having all around excellent headphone output with near zero output impedance making it good fit for any headphone.
Very well priced Sound Blaster Z actually has very good D/A converter (that DAC) but headphone output is quite typical for sound card.
So adequency for AKGs isn't that certain.
At least for classical music with high dynamic range meaning lowish average signal level (used for setting volume) and then transients and moments with lot higher sound level demanding lot more power.
Though game sounds don't have such dynamic range, because it would be really annoying to play game, if you had ears almost ringing from gunshots once shooting match starts.
(or you wouldn't hear other game sounds if volume adjusted for gun shots)
AE-5 again doesn't have such questions.
It's certainly capable to driving basically any headphone loud and clear to make your hearing take course towards premature retirement.