@SouthPark Actually, never mind. I opened your files to do a spectral analysis, and if I took your midi, it would be work for you and for me to find the correct sections to compare. I just found a forte note that was from my instrument that was close enough to compare.
I see (maybe imagine) a upper harmonic rolloff between around 3khz-7khz that is pretty linear. It's like they made this rolloff on purpose (?). To me the stock sounds were a bit "sine-wavey" - by that, I mean if you put pianoteq on one side of the spectrum as extremely sine-wavey and VSL on the opposite as extremely sampled (?) . I perceive that your stock sounds leans more toward pianoteq in the upper harmonics and a little rounder sounding. I'm wondering if it's because the sounds are optimized for the speaker system, where those upper harmonics might get lost (?).
My recording (the one I looked at anyway), within around the same pitch range, doesn't roll off as linearly and looks a little more chaotic in the upper harmonics. or possibly the pianos that Yamaha used are prepared better - who knows?
Just an opinion. Take with grain of salt.