Reporting back on my Denon AH-D7000 experience.
I had a few early growing pains getting used to the different sound compared to my Sennheiser HD600's, but after plenty of hours (my Denons have about 100 now), I can say that I really like them.
I have encountered one or two of my albums (Dishwalla - Opaline is a noteworthy one) where the bass seems a little too pronounced, but after the first few seconds of listening, I settle in and it just sounds right. There is a hint of midrange mud with a couple of my old classical recordings, but again, after the first 30 seconds of the album, my brain doesn't notice it anymore. One thing I really like about them is that I no longer have to crank up the volume to get the dynamics. I can listen at lower and safer levels and get all the impact I want.
So yes, overall, I really love them and have no complaints. They really address the only issue I had with my HD600's, which was a lack of bass energy/punch. And the tracks that had the "clouded" mids I heard, when I switched to the HD600's for comparison, I heard the same thing with them, so I believe it's the recordings and not the Denons.
I also picked up a Violectric V90 amp as well as an Objective2 to play with. Both amps sound very good, as does my Peachtree Nova. Surprisingly, I can't tell any of the amps apart from each other (in admittedly flawed (sighted) A/B and B/C comparisons) in spite of the Nova's high output impedance, which I was expecting to affect the frequency response of the 25 ohm Denons. I asked around a bit and I believe it is because the Denons impedance is rock steady across the audible frequency band - very much like a planar headphone in that regard.
Whatever the explanation, they do sound wonderful.