I am a true novice with headphones but I've been using the AKG Q701's for about a month now with a PS Audio GCHA headphone amp from a Mac Mini source. My first impression straight out of the box wasn't good but they now sound much better.
These headphones sound very neutral top to bottom and agree with much of with the OP describes. I don't find any harshness at the top end, as a matter of fact, I would like a tad more sparkle. I think the amp might be a little to laid back for these headphones but it's hard to tell with my limited experience.
With good recording these headphones really shine, the sound stage is awesome and the bass is nice and tight and controlled but there are times when the high's are a little laid back as mentioned above.
I think the brake in period is over and would be surprised if I hear any difference from this point on. Overall, I believe the 701's was a good choice for my first serious headphones although I would like to try a different amp in a few month's and see how that goes.