Don Teach asked about the shifters on some Duo-Arts (actually both
Webers and Steinways had them).
The key bed shifter was never to operate as a "soft pedal" in a
reproducer, because it can jam the strikers by sliding the action over
against them! So there was one purpose of the shifter -- that was to
initially set the player to its "Soft" mode. It works pretty well when
regulated correctly, that being, it gives such a piano a wider soft
play latitude without requiring the regular hammer rail lift to be on
all of the time.
When the D/A is on soft play, the soft pallet closes the modulator
bypass pouch and operates the accomp #2 accordion and the hammer rail
soft pedal. That setting then eliminates further soft pedal action by
a roll. So with the shifter working instead of the hammer rail lift,
the soft pedal action is retained and you get more expression on "Soft"