Update: I went back to srh1540 after two weeks of exclusively listening to HD 800 on apogee groove. It was not even a contest, SRH1540 had more "openness and detail". They don't necessarily have more sound stage on most tracks, but the moment you put in a binaural track, the space explodes far and beyond HD800 in all directions (it gets more precise if I eq the SRH1540 to SRH940 curve). They are also brighter/sharper, and often more sibilant/piercing than HD800 when the music is very compressed (HD800 sounds veiled in 2-4khz region and upper treble by comparison). For well recorded music, they are very physical and thrilling. Both HD700 and HD800 are a lot softer sounding than SRH1540 but both of them are fairly unstable around 6khz region. Sibilance always feels uni textured. On Srh1540, I can see the different shades of sibilance, and visualize how much open/closed the singers mouth was and the position of the tongue. On HD800/700 it feels like they are always with teeth closed and hissing. I have tried HD800 on other occasions with other amps (HDV820 and some lehmann amp), and I also own a Burson fun amp to which my groove is used as a line in dac (tried NX4dsd and Geek out DAC, groove dac is miles ahead) and I actually prefer HD800 on the apogee groove. Its a current feedback amp and makes the wierd off phase treble of HD800 more correct and precise. I don't like HD800 on most amps coz of some treble phase offset (which gives it the fake soundstage a lot of people like). I genuinely think my urbanite xl + decent amp has a "wider" (not better) soundstage than HD800 for stereo tracks (it does it through chamber reverb with a significant delay), not that I enjoy it, but just stating it. I actually find HD800 + apogee groove pairing to a miniature version of SRH940/1540 + a good dac amp pairing in terms of dynamics, realism and openness (I know I'll be dissed for this, but CSD do agree with my subjective opinion).
On the contrary, I find the HD700 to be a genuinely unique and nice product, that fills my dramatization desires. It doesn't resolve particularly great, but it doesn't sound like anything else, and doesn't strive for filter accuracy. It doesn't have the midrange veil I find on HD800. And one of the most unique things I've heard on HD700 which I've never heard on other cans. The center channel is so "big" sounding, I have some idea on what causes it - the mechanical softening response (which gets out of hand and clips if overdriven), but not 100% sure. I'll try HD800 on few other recommended amps, to see if it "clicks" for me, and I'll also try to measure phase and dynamic range relations with each paring. I don't think I'll enjoy HD800 on anything other than a impedance compensated current feedback amp (apogee's other interfaces, Questyle CMA series). I'll most likely sell HD800 and keep hd700. And considering that I like HD700 more than HD800, I should probably try the Beyer T1. I initially had T1 vs HD800 on my choice list, but went with HD800 since it was more universally accepted. Turns out that I'm an outlier. Of late I also got a real sense of curiosity over the Sony Qualia 010, considering it's the upgrade in the lineup of CD900 which is like the grand daddy of what Shure is currently doing.
To give a better explanation, Srh1540 feels like the vocalist, if center panned is right next to my nose, facing towards me on a lot of occasions. Sometimes its spaced out, sometimes its not (depending on the recording and how far away the singe was from the mic). HD800 center channel feels similar, but less refined. SRH1540 has a lot more viserality, it feels like I'm the mic, and in a few songs, it feels like someone broke a glass bottle on my face and I can visualise the glass pieces disintegrating around my face, or in some other songs I can feel the hit and vibration on a drum. I don't get that on HD700, but in exchange I get a very very unique presentation. It feels like there's a person standing in front of me, facing away from me and singing. It's very unique and engaging for me when I just want to listen and not analyse too much. Like I'm in a choir and someone is standing in front of me and singing.
He describes the effect in this video (though I don't agree on him saying it is "accurate", since I've compared with personal recordings as well) -