1. Worries about the effect of Windows drivers are gone. Using my older NI Kore, clicking on Control Panel\Sound always showed that Windows had loaded its own drivers, even though I was running the drivers for the Kore, and Pianoteq showed the Kore as the sound card in Options\Devices. The Zoom setup software nudges the Window's drivers out of the way--when I click on Control Panel\Sound, the Zoom drivers are shown as the default. I do not know if the Windows drivers really ever touched the sound or were bypassed with my old system, but now at least I can remove any worries about that part of the signal chain.

2. More importantly, with the card and Pianoteq set to 24\96, the general difference in sound is immediately, but subtly, apparent. I would not call it overwhelmingly different, in the sense of suddenly hearing entirely new piano sounds. Instead, each element in the sound is a little better defined.

3. What I noticed most, after only a few seconds of playing, was the definition and presence of the sympathetic resonance--I seem to hear it now as more distinct from the reverb, which is itself therefore better defined. I also sense the location of the sympathetic resonance much better.

4. Everything else, as would be expected with 24\96, has a more precise outline, particularly things that extend in time. Seems odd to write that. What I mean is that, while the hammer strikes seem a bit better defined, what I notice more, of course, are the evolving elements and changing levels. As would be expected. One result is that I notice the effect of small parameter changes much more on things like the Direct duration.

5. I want to be careful what I say here, but because the separation and "directionality" of the elements such as the reverb and sympathetic are improved, I have a better sense of the piano sitting in a precise physical location. I have not experimented yet with what this means when moving mics around and working with the reverb. However, one thing that I think I hear is that when setting the initial delay in the reverb, I can tell a slight difference--the separation between that first return and the other vibrations is more distinct.   

6. I probably shouldn't try to quantify the added realism and expression. Maybe 10-15%? Saying more might  be an exaggeration and I can imagine someone hearing less of a change, since it's a really a matter of subtle improvements in most of the elements. Certainly not a single glob of sudden sweetness. But the overall effect is hard to describe--the combination of every small improvement creates more than the sum of their parts.   

Has anyone else made this upgrade recently? Impressions?

(More generally about the Zoom:

Of course, the financial factor comes into play. I ran across the Zoom on sale. Praise be to Amazon gift cards and birthdays and Father's Day... 

Seems a bit like underkill, since it's easier to edit a track on a computer. But there are advantages to this and similar units:

1. Eight inputs including a mic and amped guitar input. Very good for just kitchen table recording of drafts and for overdubbing several instruments at once onto a drum part or piano part.
2. I can keep many things plugged in at once--synth modules, other keyboards, a mic, a guitar. 
3. Since I can keep so many things plugged in at once, I can easily record my hardware stage piano directly into my computer at any time. I rarely use the piano sound on the hardware keyboard, but it's there for quick drafts and its organs are good. I'll also be able to easily do tests on the piano samples.
4. Has internal drum patterns that are fine for drafting or just as a metronome of sorts.

All in all, more expensive than I like, and it has probably been superseded by something that will do more for less, but the results for me are still good.

Two negatives:

1. So far, I have not been able to find a way to assign the sliders to midi cc's outside of a software sequencer. By default, when using the Zoom R24 as a computer interface, all of the sliders seem to be assigned to modulation1\pitch bend. In Pianoteq standalone, if I assign one slider to control Unison detune, for example, they all control Unison detune.)

2. There are just two controls on the Zoom driver's options dialog box: the Sample rate and bit rate. The Kore software was very good--it allowed me to test various settings and made suggestions about what to try to fix problems. On the other hand, I have had no problems with the Zoom.)