100% agree with your thoughts on overwriting a factory sound - Exactly why we haven't tried the earlier suggestion. Even though this video was done on SD40, it works the same on SD90 regarding user voices.. https://youtu.be/TuyCHsfSrSE

The catch is accessing the user voices in a style. That seems to be the missing piece for what you would like to do.
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Curt
https://immusic.co
MIDI, Music and Keyboard Fun!