I had the AD700 for 3 years before I got the Q701. I did use it for music, the detail and soundstage were their own brand of fun (guests who tried them usually said something like "Woah! They sound like speakers!"). I think the AD700 has good mids and a bit bright treble spike (this helps detail and soundstage), but the extension into sub-bass and high trebles tapers off in volume and overall the headphone sounds pretty lean. I liked that for FPS games and some music genres (pop, some rock, folk/acoustic, jazz, classical), but my listening experience wasn't as emotional and involving as with my Q's and I'd wager most people would like bigger bass. It was also very lightweight with low clamping pressure so I found them very comfortable (once I bent the headband till the Earpads laid flat against my ears).
The K612 is almost the same price as a new AD700x, basically you'd hear as much detail but a bit less soundstage, much more firm sub-bass extension, very balanced while I also found it fun. You would need to crank up the volume a bit more, but the SB Z should be okay (but like all higher-end headphones, a dedicated amp civilizes and refines the sound while giving the bass a firmer body).