oddly I do find the utopia favors lower Z output amps like many SS amps. The ECP 3F is a great example, if you go tube you will be rewarded by choosing a transformer output amp over an OTL. Unless that is you like big pillowy bass that is large but lacks definition and transient attack
I had not purchased any headphones for about ten years. I just set up my headphone system in my library: Ayre QB9 DAC, Woo WA6SE. I retired recently. I was enjoying comparing the many headphones I have. The Audez LCD 2 are nice, but the Beyerdynamic T1 really win for me... for natural, large sound stage and musical. I use Ultrasone Edition 8 for travel. I also have an A&K SP1000 DAP For travel. Got to thinking I should try some contemporary headphones. When I read how efficiency of the Utopias are I bought a pair. Great decision, they are very involving, great slam, richness, coherence, speed, and balance. Like most of high end audio, if you haven’t upgraded for ten years the reviews are discussing nuances that are far above the performance characteristics of the old technology. So, while the slam is criticized on the Utopia, it is still significantly better than the older tech. They sound way better on my A&K SP1000 DAP than anything else also. i am not in this as a hobby to evaluate and buy stuff, but to enjoying what I have. These have very much taken the center place for my library and travel. Excellent headphones.
When I took the plunge and bought the Utopias I sold all four of my other headphones and an amplifier to offset the cost. No way I was going to listen to them once I had the Utopias.
I'll have these on my head and forget they're there (distracted) and a sound will come from, say, 8 o'clock, from something I'm listening to through the headphones, and it'll startle the crap out of me because I'll think someone just came up behind and to my left. Has happened more than once. They're so darn real.
I feel the same way, mostly. I'm still keeping my HD800 for the time being, mainly because I've grown attached to it, but also because I like it's soundstage and confort. Despite all of this, the french has been getting all my attention as of lately. As you've said, the way they sound so real, and for me, I'd add the word "effortless". It really can render sound out of nowhere with great speed and definition, something I'm yet to feel in another pair. Since we're still amidst a crazy pandemic time, I'll wait for things to settle down and get a better cable for it, just so I can use it more freely. Aside from that, well, I'm amazed by it.