I would like to respectfully disagree with this. I personally believe that the HD600 is by far the most neutral can available (possibly moreso than the big contenders), both proven by technical measurements and also based on my testing.
I have listened to all the models mentioned except for the K702 which I hope to check out soon. I use ADAM A7 monitors which in my opinion are extremely well balanced monitors and highly respected within the audio community. Of course, if you're using NS10s or similar in the studio, you may have become accustomed to a different sound signature and therefore my feedback may be of little value. All comments below are based on me listening to the headphones myself and then looking at the graphs later, the graphs below did indeed represent exactly what I heard on each which is why I trust Golden Ears measurements.
DT250: Close to neutral but with big rolloff in the treble. This is extremely noticeable, there's no way I could judge the treble on these.
SRH-840: Close to neutral although has a boost in the high frequencies. Not too much brighter than my monitors here, but you just need to compensate for it a bit when mixing.
SRH-940: WHere's the bass? Might be a good choice if you are planning to EQ them and can bring back the missing bass because otherwise these are really neutral for a closed can.
HD-600: THE reference headphone, very close to flat frequency response. These sounded closest to my monitors during testing and I hope to get a pair very soon to do detailed comparisons in the same room with my monitors and SRH-840s. The HD-650s are wonderful for listening but lack the detailed and neutral treble of the HD-600 as the HD-650 is more rolled off and tame.
K702: Seems to be bass light and treble happy ... can't say that this graph is accurate until I hear them to be honest though.
DT880 (600 ohm): Quite neutral except that big boost in the treble. This makes them harsh in the treble even for material that is mixed without excessive treble. I can easily see myself creating mixes that lack treble with these as I would be cutting it to compensate.
For me it's SRH-840 (closed) and HD600 (open) at present. Potentially the Brainwavz HM5/Fischer FA-003 will take the lead on closed neutral cans once I hear them.
All the best
That dt250 graph there is sure to be the 80 ohm version. Take a look at these...
Heres the 250 ohm...
Then the 80 ohm with the rolled off treble
I myself have owned both and kept only the 250 ohm version in the end because they sound like they measure