bacobaco, this suggestion may seem like the cure is worse than the disease, but if the marimba is
really that important... and you can't re-normalize the marimba sample in a DAW, and re-import it... and the other (far better) suggestions aren't getting you where you want...
Perhaps you might adjust the gain of ALL your other Nord patches/programs (including organ and piano)
down to better match your marimba's volume? Yes, your signal-to-noise ratio may take a hit, but you seem desperate for a fix.
This assumes that your amplification is capable of compensating for the overall reduced volume, of course. If not, then disregard.
