Welcome to head-fi where you will seeing diametrically opposing views/descriptions of the same headphone.
That is an exaggeration: they are not diametrically opposing views.
1. With the given track, the boominess of the IO-12 is less apparent.
2. The quote from
@hutzelmeier was
> " a somewhat similar soundstage, a surprisingly similar tonality, and sufficient detail"
- I can see where does that come from, but I'd say that for me the tonality is not similar in the bass, and sufficiently different elsewhere, too. The rest I agree with, so it cannot be diametrically opposing view.
I gave it a try myself, too, using a HD650, a Stax X9K and a Phenomenon Libratum V3 and V5.
I like (my modded earpads) IO-12 more than the HD650 in most respects, but it doesn't hold a candle to the e-stats IMHO, which present far better layering, nuance, body, dynamic details, location cues, bass resolution, fluidity, velvetiness etc. etc. I use a pretty SOTA e-stat energizer, though (~6K eur value). I think I'd like the 800S more, too, than the IO-12 (when used from another SOTA LD-MOS headphone amp that drives it well).
The closest sound to the IO-12 IMHO is still the D7200, they match pretty well, except the Denons sound more fluid and more analog, if one may say so, with less bass boom, but also smaller sound stage (in stock form). They both respond very well to ear pads optimizations.
All in all, after the earpad mods, I'd say the IO-12 is a better buy, if it passes your personal threshold for good sound.
The T+A ST can also sound more fluid than the IO-12, but the tonality and sound stage are sufficiently different that someone will likely be able to tell which suits better their taste and use cases - of course YMMV.
But these are mostly futile comparisons - even the fact that people do actually compare headphone systems of this level (~4-12x price difference) with the IO-12, speaks volumes for Dali. We have come far, indeed.