I'm one that doesn't agree with
@yangian about the HD600, yes its more expensive and its also not quite as easy to drive as the HD58X but since the treble of the K701 does not bother you it might be okay. If anything I think the HD660S is more of what you are looking for but its even more expensive than the HD600 which is my main problem with them.
As for the headband, extend out the sliders all the way, and only bend the slider/metal part. You might also try to check on youtube since I think there used to be a video on how to bend the sliders.
the are within the yellow line is where you want to bend a little