Are you saying your D3 note is outputting velocity 127 all the time?
In that case as a stopgap measure, you could create a rack to filter your keyboard input. In this rack, create two routes:
- from MIDI input to MIDI output, with one MIDI filter:suppress events --> Note D3
- from MIDI input to MIDI output, with two MIDI filters in sequence: a) suppress events (suppress all controllers etc, allow only note D3), b) Velocity/Controller Curve; set maximum output value where you want it to be.
Now your D3 will at least be as quiet as you set it to be in filter 2b - but no dynamics (if your keyboard only outputs 127, Cantabile can't guess what velocity you meant to play), so there's no way around your having to fix the issue at a hardware level.