FWIW the X9K are my new favorite Stax overall, if price was not a factor (it is).
The comments about the 3-blob and slightly diffuse soundstage and perhaps too much leading edge are ringing a bell and likely founded (not really bothering me, though). It's not a reference neutral presentation perhaps, but it's close, and it's very pleasant with their relaxed dynamics and harmonic richness in that big head space. Some people I know tell me they love it, some others don't as much (preferring the SR-Omega or bits and pieces from others). I thought everyone would love the X9K, but no such thing yet.
To my aging ears they are not as bothering as the comparatively thin and lifeless sound of the 009/S and I like them better than the HE90 (not if I'd buy one anytime soon, as it's EV price range). For me, the X9K are completely enjoyable with my preferred genres (acoustic, jazz, small chamber, orchestra, pop, rock, indie etc), more so than the 007 Mk1 or Mk2 or Lambdas/Gamma with any mods, though not the best price/performance ratio. That still has to go to my Libratum V3 and V5 (by far), which both are very close, better in some aspects (body, mids, bass impact at different frequency, focus, treble perhaps more organic) and slightly behind in others (efficiency, build quality, soundstage height, clarity/resolution, overall presentation), though YMMV and it's also genre and source/upstream dependent. (It's pity I haven't heard about Dima in a good while - no idea what happened, if you know something, Spritzer, please tell, but I have to assume Phenomenon is out, unfortunately, so you can consider the references to the Libratum irrelevant).
I have yet to hear the CRBN, but based on what I read and hear around, might be so different, that they're catering to different preferences, and likely not mine. Will see, but likely I will wait for their next version.