I have been doing a little A/B/C comparison with my W1000Xs and my HD650s and K701s and ...
Take a major Choral work like Bach's Mass in B minor, which is not something I listen to for fun, but I think it illustrates a point about all 3 of these headphones. The HD 650s are the only one of the three where there is a very distinct left ear right ear separation - very distracting and divides the work up in an unnatural way. The K701s have width and detail, and they unify the music unlike the HD650s, but unless this 1961 recording was made in a vacuum chamber, there is no warmth in the sound which one would expect from a large choral work. The W1000Xs ...perfect, but would do even better with a better recording. The music sounds natural in the same way you would hear the live performance with no left/right headphones characteristic. The other big difference compared to the K701s, is their 3D soundstage. It is a night and day difference if the recording has depth in it, and it is addictive, as it creates space, which in turn creates detail.
Now the bad part. I tried my Beatles 1 album, and couldn't enjoy it. The W1000Xs have no tolerance for these types of 60's recordings. Take out the HD650s for this album!
The HD650s have a 'tighter', more cohesive musical presentation to me, which is largely a result of their smaller, but still good soundstage. The HD650s place a different emphasis on all parts of the mix based on their importance in the recording. I find the W1000Xs, give a more equal emphasis to all parts of the mix. For Choral and Chamber Music, everything is more or less equal anyway, so this doesn't create an issues, ...but if the music has a drum set as part of the group, for example, you will get a 3D view of playing the drums, cymbals, etc. in that recording ..and be able to imagine which one is being struck and where it is in the set.
The K701s in comparison have a wider but far shallower soundstage than the W1000Xs, they color the music less, and IMO are at their best when music features a solo piano or orchestral acoustic instruments. When more instruments come into the mix, I prefer the W1000Xs. That being said, I like my grand pianos straight up with no sugar or cream ...if they are out of tune, or if the upper registers are clanging a bit ..so be it. I like to hear exactly how they sound, and this is what the K701s do supremely well IMO.
One other test I did was to try the W1000Xs out of my Total BitHead. No surprise that they could be driven comfortably on Low Gain. What was a surprise to me when I loaded some classical music I knew well onto my iPod, was that the BitHead seemed to add some brightness to the sound that was noticeable, and to my ears not desirable as directionally, it was moving the treble of the W1000Xs towards a slightly "tinny" sound. My conclusion from this brief and unscientific test, but also based on how the W1000Xs sound through my RWA Isabellina HPA with Macbook Pro USB out source, is that I would recommend checking this out carefully yourself when you are pairing an amp. with the W1000Xs and don't audition them with a warm sounding amp/DAC and then take them home to a completely neutral or bright amp/DAC combination. A little warmth in the sound adds body w/o losing any detail. Sibilance I would expect could also be a big issue with some amps. paired with the W1000Xs, combined with treble that could sound "tinny".
Unfortunately, I don't listen to many of the music genres that a lot of Head-Fiers do, and so please also consider this in reading my comments.