Hi, dnnaudio. I probably overdid it on the rhetoric by saying I had a little bit of a "buyer's remorse." To ground it in context, I'd been deliberating between Z1R and Utopia for weeks. But given that I was going to use the cans more in the office, I went with the closed cans and thought I could live with losing a bit of treble finesse and detail. But after I got the Z1Rs, though I greatly loved the warmth, I couldn't stop thinking about the finesse and transparency of sonic detail that I'd heard via Utopias and felt a pang of "buyer's remorse" whether I shouldn't have gone with the alternative. (This said, I do think even in stock form Z1R does certain things much better than Utopias, but more on that later).
With the Wireworld NPE swapped in, that "remorse" just vanished. I won't get into more details before I listen more and let novelty factor wear out, but that is exactly how it is for me now. If someone were to offer an even trade between my Z1R and his/her Utopias, I would now hold onto mine knowing that there's much more to these Z1Rs, and I'd have "remorse" the other way around!
In terms of warmth and "natural tuning," you bring up an excellent point. I'll corroborate further here but I want to say unequivocally there was no warmth lost. The tonality and gestalt we all love about Z1R are retained. Just initially, I was overwhelmed by the sheer amount of extra detail retrieval. Pianist Piotr Anderszewski has a new recording out and I could hear him mumbling phrases to himself while playing the Schumann Fantasy much clearer, which was unnerving. And because I was picking up so much details, when I was listening to a Royksopp or Aphex Twin track, I was noticing a lot of sonic artifact I hadn't noted before.
On tonality, if I can make a ham-fisted analogy: if the Utopias were a piano, I'd say they're a Fazioli or a NY Steinway - brilliant sounding, impeccably designed, de facto top of the class in sound. But I'm by nature more drawn to a Bechstein or an older Hamburg Steinway - darker, more brooding in the bass, mellow in the midband, a bell-like singing treble - Z1Rs remind me of this sound signature, as generalized and trite as I make the analogy. The Wireworld NPE doesn't make the Bechstein a Fazioli. Rather, it's more akin to trading your baby grand Bechstein to a 10-foot concert grand Bechstein. Same sound signature. You just hear a LOT more, with better control, resolution. And the treble now sings with a purer, less restrained voice.