K701 here.
Yes heard very good reviews for K612 and how flat they are,will test them.

 

If you end up liking the sound, consider looking for used K601 - both models are very close in their signature (same driver). I got mine K601 used for $100.
You can also improve depth of your K701 by getting K712 pads. The lock mechanism is backwards compatible.
http://www.thomann.de/gb/akg_k_702_gel_ear_pad.htm?ref=search_rslt_K712_320268_2
Gel-pads are used on K712 and K702 anniversary. Their profile is flat, as opposed to K701/K702 angled profile.
K601 pads are also flat profile, and are much cheaper.
http://www.thomann.de/gb/akg_k601_ear_pad.htm?ref=search_rslt_K601_245232_0
Again, compatible with all mentioned models.

 

Last edited: Feb 20, 2016

Yes,read about the test with the pads on some hifi page,not long ago,quite interesting.
AKG has a funny way or pricing their headphones.
I have read many reviews stating k612/K601 are serious headphones at a low price,not worse just different sounding.
Seeing this graph they are indeed rather flat,just tad less air in the upper frequencies(compared to K702) and have a tad more bass presence which is good.
Its probably the build quality that keeps it at lower price and the lack of a detachable cable,which doesnt really bother me.
Sonically they should be damn good.

 

DIY best headphones

 

Yes, they are!
Only 16k region is a bit recessed, compared to K240, but from 100 to 10000Hz, it's almost flat line.