I own the Annihilator 2023 and firmly believe it to be a better buy than X9000, which I've also owned temporarily in-house & tried with 3 different estat amplifiers + an energizer off my Bryston power amp taps.
I know the headphone game like the back of my hand and own/ have owned HE60, ES-1a, VOCE, CRBN, SR009 & currently also have the SR007A on longterm loan.
The issue with E-stats will always boil down to 2 things:
1. Inadequate dynamics to be classified as "endgame". The most dynamic estats I've heard would be HE60/ HE1. STAX in general are more ethereal and have great microdynamics, but more diffuse-field and light on their feet, therefore not much weight or slam. SR007 & X9000 to a less degree remedy this by having a midbass hump which is tasteful, but you will always have subpar low bass, even if driven off the incredible T2 amplifier ($12K+)
E-stats generally lack PRAT and impact, although this is more of a STAX-specific voicing compromise more so than limitation of electrostatic options on the market. STAX are also notably mid-forward, for better or for worse (can be ever slightly shouty, except 007 line and older Lambdas).
2. Amplifier selection and good source. To have an endgame e-stat rig, it takes commitment & especially $$$. No other way around it. You definitely need to build a chain around it and said chain will at some stage either require some tonal density (by means of R2R DAC, tube pre into your energizer or otherwise a tube amp). There is no other way around it (unless using DSP/ EQ, but that's another topic; ES-1a soars to my #2 fave of all-time e-stat with convolution EQ)
I genuinely find the Annihilator 2023 to be a more accurate and engaging sound representation of music than X9000, though it will not have the same detail prowess as the over-ear flagship estat (spoiler alert, almost no headphone let alone iem matches it there). That being said, Anni is more controlled, less shouty and less thin sounding, which really carries it to a more mature level of playback all while having totl resolution throughout its FR.
If you want a similar sound to X9000 in iem, it's the KSE1200 - especially with KSE1500 and some mild EQ'ing with its built-in DSP. There's no better iem comparable really.
Nobody talks about that iem much, but it cracks my top 6 along with Storm, Mentor Multiverse & Z1R. #1 being Annihilator 2023. Annihilator 2021 would be tied at 6 with KSE, just to give you an idea of the small gap in preferences at this point - they are all wonderful and world class products.
For e-stats I've extensively heard, this is my ranking:
1. HE1
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2. ES-1a with convolution filter
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3. SR007mk1 (S.N 71xxx range)
4. X9000, HE60 (mint drivers and O-rings) or SR009 with convolution filter
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7. SR007mk2.5/ 007A
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8. Lambda Nova or ES-1a stock form
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10. CRBN & VOCE
Hope that was somewhat helpful & not too overwhelming lol