I'll spare the dedicated AT fans wading through my waffle and summarise them thus: Imagine W1000s with more treble, or W5000s with much more bass and a bit more treble, but still with the forward mids that are the AT sound signature. Both were on the table too so I could compare them, but I didn't do so comprehensively, but only enough to get the primary tonal differences.
I finally managed to get a few hours to myself to head into the city, have a relaxing lunch and try out the W1000X in the Best Denki, which has a high-end headphone listening table. When I arrived, they were plugged into the AT-HA2002 and sourced from a Sony SACD player. I didn't note the model as I've become a source snob and consider just about anything sigma-delta to sound harsh and digital. Ignoring the inevitable fact that my the classical tracks on the CD I brought with me were going to annoy me in that regard, as well as a lack of familiarity with AT amps, I concentrated on what I could of the sound.
What AT seem to have done is merge the new X frame and pads with the W1000 cups to produce an interesting hybrid that fixes most of everything that annoys me about the different ATs in sound, while adding the annoying fit of the X range. In short, they are good if you have a big head and will dig in under your ears and not seal if you have a small head, requiring either some brutal and irreversible bending of the arcs, or some careful re-shaping to get a good seal. Unlike the A1000X and A2000X, however, you don't feel a need to push the cups inwards to get enough bass, as, hallelujah, they have BASS, and a serious whack of it at that. Rounding up the design, the cable is the same soft rubber OCCC cable of the other X series, but terminated with the funky wood plug you see on AT's woodies.
Shotgun summary for those familiar with ATs already: Imagine W1000s with more treble, or W5000s with much more (possibly Denon-level, but better quality) bass and a bit more treble, but still with the forward mids and the drop in the upper mids/lower treble that is the AT sound signature. Both were on the table too so I could compare them, but I didn't do so comprehensively, but enough to get the primary tonal differences. I admit I'm probably not that great at quickly determining some of the other abilities, such as speed, with headphones and really need some time with them at home.
What struck me most is that is that because of the very forward mids, they will be somewhat annoying to listen with using poor equipment. For me, I hate mids so forward, as it makes a lot of music sound tinny, as well as making the headstage seem much smaller. However, with the W1000X there is a lot more treble and a lot more bass than what I'm used to hearing from an AT. The A2000X to me, for this reason, sound like they are all over the place, in the wrong places tonally, in a somewhat similar way the HD-650s do to me, excepting that the HD-650s have much more bass. I think the W1000X would rock balanced on my smoother-than-a-baby's bum rig, but I'd still wish for slightly less forward mids and a bit more in the upper-mids -- around 6.3k where people find the HD-800s annoying. The Headroom graph below (for the W5000) shows it well. They are though, for me almost there tonally otherwise. If you don't want all that "LETS PARTY!" bass, but want more treble than the W5000s, there is always the A2000X. Pity about the poor fit though.
Here are the notes I made on my iPhone while listening, cleaned up so they make some kind of vague sense:
Busted (dZihan & Kamien): Good bass punch. AT vague upper mids show here.
Monsoon (Jack Johnson): The deeper bass comes through clearly along with some mid bass.
2nd choice (Marti Jones) sounds rather tinny because of the forward mids.
Tin Pan Alley (Stevie Ray Vaughan) bass comes through strongly and sounds glorious because the mids are mostly all guitar and Steve doesn't sing so close to the mic.
Serves Me Right to Suffer (John Lee Hooker) sounds rather boomy.
Chopin's Berceuse in Des-Dur, op. 57 (Vladimir Ashkenazy): Badly recorded Chopin that has glare (?) is irritating, emphasizing the effect of the mic being possibly too close to the piano and digititis in the source. Ditto classical and jazz.
The Body Acoustic (David Chesky) fares better with more space around the instruments.
