I'm surprised you rated the K701/702 so highly. It's never really impressed me for gaming at all but I don't have the Mixamp and just use a desktop amp. Everything just feels so slightly distant for gaming with them and it's hard to get into the game when it's like this. Everything else is OK and I don't mind it's huge soundstage. I myself would take the K601 over the K702 for gaming anyday and the K601 is one VERY under-appreciated headphone for gaming. The K702 just has more detail and a better soundstage, but poorer imaging. I always felt that what detail the K601 did offer was more forward sounding. K601 has more forward mids than the K702. I had both for quite awhile. K702 is better for music to me however, but I prefer vocals on the K601, but not enough to keep them.
AKG K240 Studio I 100% suggest to anyone that wants a CHEAP alternative to the HD-555 or the AD700 is a poor fit. It's only $99 or so and semi-open. It's even very good for music.
I don't know if you plan on reviewing other headphones in the future but I'm pretty much blown away by the Audio Technica ATH-AD2000 for gaming. Maybe that's why I can't enjoy the K702 for gaming. The details are just so much easier to hear on the AD2000. The sound is just more immersive. In the last few weeks I haven't been able to go without them for gaming. A new cable helped my K702 for gaming, but not enough. When I take off the ATH-AD2000 and put on the K702 for games to compare them, I'm pretty much disgusted. I couldn't stand the lack of bass on the AD700, but love the bass on the ATH-AD2000. It's amount of bass is perfect for everything but bass heavy music.
I also would point out that if anyone found the AD700 to not fit them (like me) the ATH-AD2000 might! They have more clamping force. They're also great for music too obviously. They do have slightly forward mids, which is always something I like for gaming. I have a feeling that the DT-880 might have better imaging, but the ATH-AD2000 will have a better soundstage and mids. I imagine slightly more bass, but I'm not sure.