One experience I would like to share with everyone. When I was auditioning the K601 and K701, and deciding what to buy, I had a ton of music with me. To mention a few: Pink Floyd Pulse, Riding with The King (BB King, Clapton), Sultans of Swing (Dire Straits), Pure Jazz (collection), The Girl In the Other room (Diana Krall). I had already decided to buy one of these pairs, since I have another AKG pair, and I am very pleased. Now, I was aware of the "Rock Issue" with them, since I listen to rock/rock&roll/blues quite often (also Jazz, Classical).
Both pairs had around 5 hours of total listening done on them. Both driven from this setup: Marantz CD player (seemed quite good) -> Marantz Integrated Stereo Amp (with good headphone out) -> Headphone
First the K601: They sounded very good. I heard most of the CDs (like a minute each) and was quite pleased with the way they reproduced the whole range with Rock, and Jazz i have to say. Deep impactful (not too much) and detailed base. Good mid range (the Rock vocals were great), and detailed but not annoying treble. Excellent soundstage (very airy)
The K701: Somehow, i started off with Diana Krall. MAN! If you have the K701, try listening to Girl in the other room! Very detailed Base going ridiculously low, Diana Krall sounded like she was whispering over my shoulders and and the treble was excellent. The soundstage was in another world. However, i did sense a tiny bit of roughness. When I moved on with Rock, things started changing. Riding with the king was kind of harsh and bright and not what I expected, and Pink Floyd, to my big disapointment sounded very mediocre. However Sultans of Swing sounded very good, the whole range was excellent (especially vocals).
The reason why I chose the K701 is because after doing some research, i realized that with a good burn in, they would loose that roughness and become slightly more engaging. Also, unlike the K601 which was pretty good with everything, the K701 was absolutely amazing with one at least two albums I heard. I guess the quality of the recording (mainly the mastering of the album) has a lot to do with what you get from a headphone, since you get all that detail 2 centimeters from your ear.
Its been almost 100 hours of listening (+burn in with music), and I have to say I have noticed slight improvements. Rock does sound much better than it did, and this has nothing to do with "getting used to the sound". Some people say to give them around 300 hours, and that is exactly what im doing. So far, pleased with results.