Last year at RMAF I got a chance to hear a balanced K701 on the Bryston BHA-1 at TTVJ's table. I was blown away, and I honestly thought it was one of the best sounding systems there (short of the SR-009 systems anyway). I also heard the same K701 with an adapter on the BHA-1 from the single-ended output, and while it was good it was much less impressive. For some reason, the balanced output really brought the K701 to life from a dynamics standpoint. I'm still not convinced that balanced cables make a huge difference for headphones -- but I can definitively say that the balanced output of the BHA-1 sounded better than the single-ended output.
One problem with the K702, Q701, and K702-65 headphones is that they have a three-wire detachable cable -- so unfortunately it's not very easy to go balanced with these headphones. You'd have to do some fairly significant modifications to get the headphones to accept a balanced four-wire cable. By contrast, the K701's cable is hard-wired, and it actually has four conductors and is therefore quite easy to balance (just cut off the TRS connector and solder on a 4-pin XLR).
Out of curiosity, has anyone taken the K702-65 balanced?