I think the Q701 is a step above the K550 and even the KRK KNS-8400 (not a huge step going from 8400 to Q701). The Q701 with my setup has a similar sound as my KRK KNS-8400. The Q701 just has a very slightly clearer sound, larger soundstage and more forward upper mids. Honestly it does feel like the Q701 has more bass than the 8400, but I will compare them side by side soon. The 8400 right now seems like it just has more mid-bass, but slightly.
Here's something that may be interesting for some. I was playing Skyrim today and used my KRK KNS-8400 instead of my usual Q701. I was very surprised that it sounded almost the same! It felt as if I was playing the game with a closed Q701! Here's what surprised me the most. The sound was much fuller sounding and it felt as if the KNS-8400 made it a little more immersive and realistic. Felt a bit warmer than my Q701, which was such a surprise. Everything definitely sounded like it has more texture to it. Despite the smaller soundstage it was still quite large. There's a few example of sound effects in Skyrim that sound so much better on the KRK. Stuff I never really noticed before.
Basically the KNS-8400 would be one of the best closed headphones I can think of for gaming that's fairly cheap, as long as you don't need tons of bass. I think both the Q701 and the KNS-8400 have a similar amount of detail. Both are detail monsters IMO.
Now to make matters worse, every K702 I had never sounded like this Q701, so I don't know if the 8400 I have will sound like the K702 or not. I always disliked the K702 for gaming due to it's goofy and not very accurate soundstage. Everything felt more distant than it really should be. I've owned 3 K702 before and they all sounded the same. I won't open a can of worms and compare the K702 to the Q701 any further
BTW It seems these may be somewhat harder to drive than I thought! A clip can drive them quite well, but you have to max the volume. That thing drives my headphones better than my portable CD player, Fuze and possibly my Ipod Touch!
I was checking through all the graphs on innerfidelity and lists all the power requirements. If I'm reading it right, the 8400 is even harder to drive than even the K272HD! K272 is even harder to drive than the K271 MKII. Thought they shared the same driver but maybe not.
I actually didn't realize this requires a bit more power than the 6400.
Edited by tdockweiler - 12/20/11 at 3:21pm