Well, I owned the X1 not too long ago and the K612 is definitely the more balanced and less bassy but to my ears, it offers the best of both worlds. Lots of immersion [very dynamic sound] but with great imaging and tonality [neutral and very holographic].
It really a very special gaming headphone [and a decent music can as well].
I suspect it's very hard to beat in terms of gaming performance + sound-whoring/immersion blend... I am not sure my soon to be HE-560 beats it here. It surely will in sheer music performance but for gaming purposes... might be a very interesting comparison [one I am eager to make].
Provided, you amp the K612 at least a little, that is.