To this day I still love my Z1R and as the market evolves, the Z1R's value continues to grow - goes to show that the multi-kilobuck scene isn't growing (though the upper-mid to Hi-Fi range is increasingly competitive 1K - 1.5K)
Z1R remains a "GOAT" when it comes to bass, still outclassing the likes of some of the best overall sets I've heard or owned like Mentor Multiverse, Annihilator 2023, Storm and proclaimed "bass" sets like Maestro SE, Legend Evo & Singularity.
That in itself is impressive seeing that it's from 2017, but the fantastic part about Z1R is that it's not a one-trick pony. It's one of the best at dynamics (especially macro), has a holographic and enveloping stage, extremely well-textured treble as well as bass & its mids are better than people give credit for. Its weakness would be a generally less lively lower midrange tone, though it's still fine, just that the BA driver is less special than the dynamic counterparts.
I also own Volur, and personally do believe it is slightly better overall but it's more of a case of them trading blows. Now value adjusted, of course the Sony is a better buy, but the Volur is a more refined and versatile set, though losing out a bit on engagement and the sense of grandeur the Z1R has. The Volur is a bit tighter in the bass and definitely hitting harder in the sub, but less weighty and rumbly than Z1R in the midbass. It is more even-keel in the midrange, forgiving in the treble, but wispier in the upper treble/ air which sometimes adds a certain effect of artificiality on poorly recorded tracks. This really only being apparent beyond ~13.5kHz and especially peaking at 15kHz, so for some this set's treble will come across as quite a bit darker than others if they don't hear the air boost. Volur really is a weird love-child of other 64A products (U12T/U4S with slight less midbass than Nio; though outright better than each individually) - 64 Audio's house sound is consistent in sounding like a clean monitor mid-to-high with slightly forgiving mids - it's not always the most exciting and can sound thin on some models. What makes the Volur my favorite is they added ground-breaking (or shaking) bass quality.
One part I commend on Volur is that it's not only generic off the shelf drivers being used, but they've had a fully custom DD unit made as well as waveguides installed to their tia super tweeter. This is engineering at work which yields a different result than anything before in that it is extremely resolving with clean transient lines. The midrange is, like the U4S, the range that doesn't keep up quite as nicely.