We've had an X3500H for about 3 weeks now, changed from a Pioneer VSX-1131 with MCACC that developed a problem and was returned.
I must say, the audio quality sounds very noticeably better and the surround effects of both movies and music are much more pronounced.
Dynamic EQ does a great job making music sound good even at low volume levels.
Today my partner said unprompted that she doesn't need to adjust the volume during TV shows as much anymore either, even though we have Dynamic Volume disabled. I speculate that could be because of Dynamic EQ as we don't usually watch TV super loud.
Audyssey XT32 has done a great job with my annoyingly asymmetrical room layout, and my sub sounds more "full" and integrated with the other speakers, although I have changed the location of the sub since changing AVRs so it's hard for me to say how much of that improvement is as a result of Audyssey.
The only negatives I would mention are that I find the volume overlay a bit too intrusive with the black background and the silly ECO thing, and stays on the screen longer than I'd like, and the volume controls are too slow with single presses and too fast when you hold the button. Also I would like it if it had the PCM frequency in the Info overlay. You can access that information but it's buried in the menus.
Also it would be nice to have a larger volume display on the front screen (it's tiny!), but all AVRs seem to make that info very small for some stupid reason.
DTS:Virtual X, which I was interested to hear after reading the specs, was surprisingly bad sounding, sounds very unnatural and metallic to my ears and I wouldn't use it under any circumstances really.
I'd be interested to see if Dolby Virtual Height that is on the X3600H is any better, but if it's anything like DTS:Virtual X then I'm very happy I didn't spend the extra money for the X3600H as I don't need the extra channels.
Actually thinking about it now it might sound bad because I think Audyssey has to be disabled when you use DTS:Virtual X.
Also if I'm being fussy, the remote is a lot larger than I'd like, and the volume buttons are a bit too difficult to find by feel without looking.
But those are all minor things and no product is perfect (unfortunately
The Pioneer drove me crazy with clicking relays all the time, so I'm very happy there's none of that with this Denon, and it has been rock solid.
Also the Denon is quicker and more reliable switching audio modes (I have a HTPC with lots of mixed audio formats, and switch between them regularly). On the Pioneer I used to have a process of hitting stop, then play the new file with different audio settings because sometimes the Pioneer would not notice the change. That mucking around seems to be unnecessary with the Denon.
I'd also like to commend Denon for allowing you to factory reset your AVR if necessary to the original firmware. There's no valid reason that firmware upgrades should be a game of Russian roulette like on my LG OLED and Samsung phone.
Very happy with the switch overall.