Sounds like you’re getting tripped up on dB vs gain multiplier.
Cantabile’s gain sliders display dB values which go from -oo to +7ish. But that’s just how they’re displayed. Internally they’re stored as a gain multiplier where -oo is 0 and 0dB is 1 and it’s these gain multipliers you need to use when using expression bindings.
If you’re trying to manipulate gain values with expression bindings, you might find the toDb and fromDb functions helpful. See here.
Also, don’t forget the sliders use a control curve that varies things. Perhaps I should expose these curves as functions as well? Let me know if that would be helpful.