Pros: Comfortable, attractive, priced reasonably.
Cons: Godawful mids that sound artificial and plastic.
This is the only pair of headphones I bought that I was never able to warm up to. The reason for this is that the mids - especially vocals - take on an unnatural, artificial and plasticky sound. They never sounded true to life and began to grate on me after short listening periods. They were OK for instrumental music, but even then, the tonality was off in the mids.
What's disappointing is that AKG dropped the K-501 and K-1000, and gave us this. The K-701/2 is nothing like AKG's previous efforts. I have the K-1000, K-340 and K-240DF, and used to have the K-501. All of those got the midrange right. I was expecting to love the K-701 as well, but like I said, the artificial tonality in the mids completely ruined them for me.
Strangely, the K-601 sounds halfway decent the times I've listened to it and I remain hopeful that AKG will introduce a model that gets the mids right. They used to have some of the best mids of any manufacturer.
I haven't heard the other AKGs you mention above so can't compare ... but against Senn 650s, beyer DT880-250, the K701 are probably the most balanced WRT freq. spectrum. The HeadRoom graph seems to point to that, too.
BTW, the SQ -- at current 160hrs -- continues to improve, but not as dramatically. (Now if I can work the same magic with my Grado 350i's, which I similarly gave up on a few dozen hrs after new (like 701s ... literally sat idle for years, until I (finally) heard about the extended burn-in time ....)
Does not matter what amplifier you are going to use this with, how long you are going to burn in for or what choice of music you are going to listen they are going to sound awful, plasticky, unnatural, shallow, uninspiring. I’ve listened AKG’s on 800€ valve amp, desktop amp, straight from PC, listen brand new 50 and 5000 hours run in headphones, death metal and classic and all their sound is not acceptable. Good look thought it that’s matter to you.