Hmm. The distortion is present inside SAVIHost, but not in the standalone. That suggests the DLL and EXE might indeed be fundamentally different software. Next step is to determine if the two are
configured exactly the same way, by using a common preset.
Often, ambient noises are user-configurable, although for pianos that usually means pedal noises, not butt-slides. However, the bench creaking might be part of the pedal noise samples. A microphone aimed at the pedals might well pick up such extraneous noises that the mics inside the piano would not.
If there's a way to adjust pedal noises, turn them completely off when making your comparisons. Not all piano instruments let you do that easily, unfortunately.