send note-off messages in chord progressions

Hello,
I have a note-off problem with polyphonic chords and kslider.

Imagine I am playing a Bach choral on my midi controller, I need to send to kslider the note-off messages when I release specific keys. I mean, I need to visualize in kslider what I'am playing, but kslider does not show the note-off messages that are produced when I release the keys . Kslider only shows
the notes held down, and once they are not held down any more, it keep showing that ON. If I use "flush" message, all notes are turned off.
I thought about using "borax " but it does not provide the specific notes that are held down in a specific moment.

Any Idea? Please?
Thanks in advance.
Sabina

I need to catch the value of every single note that is currently held down while I am playing my midi keyboard controller.