May I ask you if you tried to record those Sympathetic Resonance tests in midi, and render the sound in high quality mp3 using the 256 voices polyphony mode adjust of Pianoteq?

    The automatic polyphony mode (pessimist and optimist) try to reduce computer processing by removing the less important computation for sound, like distant overtones resonance.

    Regards

i've downloaded the demo 2.1 of Pianoteq and i've found 2 bug :

1) in a real piano, if you play a lot of keys pedal down (make a glissando), and when you keep (for example) c3 down when release the pedal up, you still hear a lot of overtones.

In Pianoteq sympathetic resonance : it doesn't behave like this. You hear
just one overtone

i've just added this feature (bug fix) in my script, available soon for AKP and GalaxyII

2) when you repedal during the release of keys, you hear a synthetic dry tones.

-> in a real Piano you hear the overtones/sustain resonance in the release, not the dry tones, when you repedal.

And your prodcut is good to use it with others piano library.
You should create a plug in version only with string resonance and other effects for other piano library.