This is an excellent recording, thanks for putting the effort into it. The walkup test at 127 velocity helps determine where the multisample cutoff points are, and a lot more samples are used in the upper register than in the lower, which contributes to the incredibly bright sound of the lower register notes. The walkup at 90 velocity would help determine the differences that lower velocity makes in the tone so I recommend that you do this test also and send all three resulting MP3's to Simon at SVPworld for his comparison page. Judging from the Moon River demo, there's not much velocity-based variation in tone at all. Also, as with the Yamahas, I'm not crazy about the short decay on the initial tones.
All in all the WK8 has a pretty decent piano sound as far as overall realism goes, but it is excessively bright for my taste, especially in the lower register. It almost sounds like someone sampled a piano then turned the high EQ all the way up to max on playback. This would be great for cut-through piano solos in a band setting, but I'm more of a mellow-piano kinda guy. Others will like this piano sound a lot I'm sure.
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Jim Eshleman