In answer to Joseph Osborne's question, does the Duo-Art piano
continue to play softly after it's done playing the series of big
chords?  If so, try strengthening the spring on the swiveling finger
on the pneumatic that pushes on the accompaniment regulator linkage.

I've seen pianos in which the accompaniment lever gradually moves to
a softer position because that spring isn't strong enough to hold it
in place.

Art Reblitz - Reblitz Restorations
Colorado Springs, Colorado