While not up to absolute top level in details because of some above neutral bass, K612 itself is very capable for gaming.
But for gaming immersion question is also about signal.
If it's standard stereo speaker mix from game, you don't even have proper left-right immersion.
Only very artificial "sound inside left/right ear or in center of the head" immersion.
Because with headphones there's no natural propagation of sounds of left side sources to right ear and vice versa.
Compare these two:
https://youtu.be/Y6ROujJ8Ae8?t=50s
https://youtu.be/Y6ROujJ8Ae8?t=6m20s
No matter how expensive and/or glazed with audiofoolery, headphones can never create binaural cues brain uses for positioning of sounds:
We hear in 3D with two ears, because head and pinnae cause direction dependant changes to signal received by both ears from sound source.
Ability to mimic those cues is feature DACs lack as dumb single purpose devices.
Whole DAC hype has been basically selling less features and functions as more.
Though at least that SMSL is well priced.
For comfort AKG has given up on those headband torture bumps years ago and flat headband should be good for hours and hours of continuous use.
Though few months ago read one person finding even flat leather headband inconmfortable.
I guess he had "pointy" top of the head.
Also with "automatic" adjustment of headband, if you have big head or small head it doesn't work as well.
With smaller head, especially downward narrowing, it could easily feel that ear cups try to slip constantly down.
That's because their position keeping relies on pressure on head.