I decided to finally pull the trigger and get the K701 after liking it better than anything else I heard at Can Jam. At the time, I didn't like it as much as I did the button RS-1 when plugged into my Arcam 73-DV 332 setup. Now that I've got it plugged into my setup, I like it far more than the RS-1 and HF-2. I also think it's significantly better than the DT990. It performs almost as well with the x-head amp I have and isn't terrible with my portable Ibasso and the Sony D321.
I don't get all the comments about the K701 being shrill and thin. There's way more variety in how things sound with this phone than with the others I own. I never notice a shrill sound unless I play a bass-lite recording at too high a volume. Even with my non-tube amps, the K701 never feels cold and thin. Things can sound very warm and full with bass drums that cause physical vibrations. Other albums can sound a bit irritating, but it's a really small list. Iron Maiden's Killers album, whether it's black triangle, UK 1st pressing, or US 1st, is probably the worst offender. Modern brickwalled stuff is more tolerable here than with grados, but nothing can make that stuff sound good.
The K701 has a lot of what I liked about the RS-1, except better. It's wider and doesn't smash up the details. I like how the first couple seconds of the Gattaca cd don't go overly loud now. Much more natural. The wall of guitars in Death's Human is also able to breathe now. With the RS-1, there's more bass in the sound, but that wall of guitars sounds a bit smashed in comparison to the K701. The vocals on Styx's Babe come out of the drivers a bit further and surround me the way I wished they would when I heard them through the RS-1.
On the RS-1 I liked how certain parts would build loud enough to sort of fly up and out of the drivers. It does create a certain sense of excitement, but it could also be fatiguing. The K701 still has this effect, just a bit toned down.
I'm not sure on the terminology to describe the sound staging. The RS-1s always felt horizontally wide to me, much more so than the vertical. The K701 feels a couple rows back and the sound moves more vertical and horizontal than with the Grado stuff. This is more of what I thought the GS1000 and PS1000 would sound like.
I've thrown a lot at the K701. Classic rock, all sorts of Metal(not much made after the year 2000), 80s hair bands and sleaze rock, RCA Bowie, lots of film scores, 90s Eurodance, 80s pop and dance, easy listening stuff, new wave, 70s punk, grunge, probably hundreds of albums. It seems to like most things. Note that I'm using 1st pressings and staying away from stuff that has significant limiting, noise reduction, and compression.
I've heard these are more of a reference headphone, but I really have no idea what reference is supposed to sound like. I see this as being my #1 headphone for the time being.