I\'d say it is excellent. The soft samples may be a bit dark, depending on your tastes, however adding a little boost to the high end generally corrects for this problem. I\'ve also tried the Post Bosendorfer, which is perhaps easier to use than the Steinway, although I find the Steinway sound has more dynamic range and prefer it for most things. The softs are gentle and dark and the louds are stormy and bright.
The added brightness on the Post Bosendorfer does give it more presence..it feels more like a live instrument than the Steinway, and the bass end is monstrous with huge sustaining tones. It is a tremendous piano and a wonderfully recorded and programmed sample, but perhaps not as intimate as the Steinway can be.
My guess is that if you want to do rock or jazz you would prefer the Bosendorfer, while for classical it boils more down to a matter of taste and the particular style.
The Brahms Piano Concerto #2 on my site was made with the post grandioso steinway:
I struggled for some time with the very question you raise. I did not have the benefit of the actual sample; like everyone else I had to decide on the basis of mp3s. In the end I am convinced the PMI Bos 16 layer model (there are several options) is the best-sounding piano sample currently on the market. Duncan HAS the Post Steinway, so he may be in a better position to judge the merits of that sample. Certainly it is a piano with great character, judging as I say by the mp3 samples. But personally, while I was initially very impressed with it, something about the sound held me back. When the mp3s of the BOS became available, on the other hand, I had no trouble at all recognizing that this was the piano sample for m3. Of course, if you have the money you can buy both!! I use the PMI 16 layer BOS for all the NON-Bach pieces at my site below, and a heavily modified version of the Steinway B (Truan) for the Bach. (By the way, the Steinway B, on its own, without any major editing and tweeking, doesn\'t seem to me as good as Post\'s Steinway. But then, they are two different models of Steinways, so comparisons are difficult.)
In the past months I\'ve spent some replies talking about PMI Grandioso libraries so you can easily find more informations and opinions by performing a search for my member\'s number or for \"PMI Grandioso\" or similar.
In addition, I strongly suggest you to visit my web site which contains lots of resources and informations about PMI Grandioso serie.