FWIW, I've had a bit of a play with the American D using try-sound.com.
I can't be certain yet, but from my testing, I don't think the American D has particularly clever voice management, and it will consume many voices for repeating notes - more than it needs to.
I have the same issue with EWQLP - it is absolutely brain dead.
The test I did was to set the voice limit relatively low (24, I think it was), play and hold a bass note, and then in the right hand repeat a three note chord, rapidly. (all without the sustain pedal) After a few seconds, the bass note was terminated, which is silly. It should have terminated an older voice that was being used for the right hand repetitions, because that would be FAR less noticable.
IF I am right, then IMHO if you set the voice limit very high, you may find that you can easily reach that limit, and start to stress your disk ("slow disk warnings"). Don't assume that just because you can reach a certain voice limit, that you NEED that voice limit (or even more). Rather, start off low, and gradually increase the limit until you feel that you've reached the point of diminishing returns. I.e - if you can't notice any increase in fullness of sound, and you are not noticing any dropped notes, then you may have reached the point of diminishing returns, and further increases are just a waste. Obviously, if you can't ever reach that point of diminishing returns, then you need to address that. (change settings, or a faster disk, etc)
I tried the Vintage D as well, and it DOES appear to have good voice management. (for example, repeating a note with the sustain pedal did not exceed a simultaneous voice count of 4 - very good sign! If I do this test using EWQLP, it just keeps using a new voice for every repeat, which is stupid)
Unfortunately the Ivory player doesn't actually seem to display a live voice count, which makes it a bit harder to know what is going on.
Also, if the American D does use lots of voices, that doesn't mean that all those lots of voices are wasteful/bad - most of it could be very worthwile. (e.g sympathetic resonance). All I'm saying is that the behaviour I observed for that repeating chord test is questionable.
Also refer to this recent account from Macy: Re: Synthogy Ivory - HDD or SSD?