While some IEMs scale with desktop gear, almost all of them sounds good from a nice dongle like RU7 or even something cheaper.
My listening is mainly with DAP or fullsize DAC/AMP.
Diminishing is strong even at the 20usd bracket, but we could argue that 1000$ is point where it's more about tuning differences and getting the very last percentages of performance. Up to each if that's worth it or not, some would even stop at the cheap EA500 at 70 usd and call that endgame.
My advice is take time and enjoy the ride, try different IEMs on the way up and you will probably learn what you love. And even consider buying used, if its wrong for you it's less of a loss when you sell it again.
But if you go for the 800$ mark all the models you mention will be good.
DTE900 and Neon Pro is more in the energetic and speedy camp, both are excellent. Love the Neon Pro tuning and coherent sound, but lacks DD. But it has a excellent timbre for an all BA, my favorite all BA. My metal god
DTE900 is super impressive with a technical and fast low end, energetic and detailed tuning overall.
Quite unbeatable at this price range if the sound is for you. DTE900 lack some polish compared to better tuned models, and has a forward ear gain that can be to tiresome. DTE is airy, but not that much compared to NP.
Ascension is the most balanced and organic sounding AüR, the balance between the low end and the rest make it warmer than Neon Pro. Has the DD that NP lacks, but it's a quite different low end tonality compared to DTE900. Ascension is more textured and natural, DTE is faster and more visceral but also less natural sounding on acoustic music.
Have no idea about how the crossovers work in the Ascension, but to me the midrange sound closer to DD than BA. More rich and engaging, used it for the Xmas vacation and the midrange made me now dislike the 64audio U4s as its lifeless in the midrange.
Highs are also good, airy and natural without being peaky or tiresome.
All 3 models have good soundstage
DTE900 very speaker like with a more forward projection that's further away from you. Have l more width than most IEMs.
Neon Pro is more 3D, has good depth and width but less than DTE900 and is closer to your head.
Ascension is also good at 3D stage and has a presentation that blends the qualities of NP and DTE900. Has also the maybe the best dynamic range in the stage where it can sound like it's more behind you and also reach far forward or to the sides.
@Scuba Devils is not alone, think many prefer more relaxed tunings and specially in the upper mids/ear gain.
Both Neon Pro and DTE900 has forward upper mids, both rides the borderline of what I find ok. Perfect for most days, but not on a bad day or with brighter recordings. This is also where Ascension is much better than Neon Pro and DTE900, has a more forgiving tuning.
I have still a new toy syndrome on Ascension, so keep that in mind. But even so it's a set that I wouldn't say wowed me at forst listen, it has grown more and more over the days to maybe be my favorite now.
And there is plenty of other good brands and models.