Okay, bought the full version and installed it yesterday. I've been playing with it. Overall, I think it's really a finely crafted piece of work. It is definitely a bright and powerful piano, though. It's not meant for thoughtful, poignant, smokey, introspective film score noodling (at least IMO). It seems designed to stand up and take charge and heaven help anyone in the way.
Definitely a place for that.
In trying to get the most introspective, close mic'ed sound out of it, the condenser mics are definitely my favorites. The tube mics sound too bright too me. There's a different quality to the ribbons that I might like and use in certain contexts. The have kind of an interesting, fuzzy character. I think the ribbons are most effective on things played in the midrange of the instrument, and probably best for simple playing (I miss fullness of the bass on the ribbons). To get a warm sound on any of the close mics, I do think you need to roll of quite a bit of high end. For me, though, if I didn't have the tube or ribbon mics, it wouldn't be a big deal. The condenser is the clear winner, IMO.
As far as flaws are concerned, there's a buzz on C6 that catches my attention, but I know real instruments do this sort of thing (and technicians often find it impossible to deal with these things). Also, it's the character of this instrument, but the highest two octaves are really quite percussive and ping-y. It would be hard to coax a singing tone out of that range, IMO.
I do think I'm forming an opinion on use of multiple mics on Synchron pianos (I have both of them). If possible, I think I'm going to prefer to pick one mic position, and just use that one, rather than mix a number of them, unless my goal is for a contextual piano back in the weeds, or something really ambient. I think what you're playing might really impact this choice. If you're playing fast, clean passages, or if you're playing clean, pure combinations (powerful octaves, fifths), using multiple mics works (again IMO). But to my ears, once you start playing complex harmonies, things get kind of trashy as multiple mics compete. I would think it's a matter of all those phase differences between multiple mics combined. And, I think it rapidly gets to a situation where you're exciting way more harmonics with multiple notes than you ever would on a real instrument, playing a particular combination of notes. I guess I'd rather just use one of my favorite external reverb plug-ins if I need more room than my chosen mic position offers.
To get a warm sound, I also experiment in decreasing the MIDI sensitivity quite drastically. That helps, but then you're simply not using the higher velocity samples. What I think also helps for a warm, close piano sound is adding a tape emulation plug in to at least add a tiny bit of noise floor. Otherwise, with just close mics, the instrument sounds too squeaky clean.
One more observation... To my ears, the una corda pedal on the Steinway D doesn't make that much difference. In contrast, using the una corda on the Synchron CFX is quite noticeable.