My impressions are similar to yours, mj. For me, the Ncore excels in what class D amps seem consistently to do well, particularly in the way it reproduces midrange ambiance and decay and thus tone. I hear a continuity I quite adore, and in a degree to which I've not heard from other amplifier types. That said, and despite other things the Ncore does well, I find its presentation a little flat, and leaves me wanting more. It's as if the Ncore, like you said, drops the finer leading edges of the music---almost as if I'm listening through a cloth that veils high frequency decay, ambiance and subtle detail.
I suspect that this quality, which I've also heard by degrees but consistently in other class D amplifiers, relates somehow to FET switching nonlinearities, dead-time and mistiming. Class D amps also make my ears ring with a subtle HF pressure. Has anyone ever talked with another while playing a 20Hz tone through a subwoofer? You can hear the other person clearly, but there's this evident pressure. I think what I'm hearing with class D amps is something of the HF version of that. Class D amps create a tremendous amount of HF noise. Most of that is filtered off at the output, but some gets through. Yes, not much gets through below 20KHz, but the human ear is imo sensitive at least a few doublings beyond that, where appreciable noise stills passes into the speaker. That noise, I suspect, creates the pressure I sense, and in some difficult-to-identify manner intermodulates or disturbs the perception of HF space and subtle ambiance.
On those speculations---the related problems of switching and HF noise---I would predict that something would have to give in particularly in the HFs. I'm unsurprised some people report hearing a certain flatness or lack of sparkle.
