I recommend keeping the softening device for your Duo-Art.  I would
even recommend putting it back in place.  It is a little in the way,
but you never need to use it.  If it is the deluxe model with the
pneumatic to operate it, you needn't recover the pneumatic unless you
are concerned with appearances.  True, it is a useless device, but you
never know what someone in the future might think.

My truly wonderful Duo-Art upright had the "crash valve" disconnected
by the former owner.  Fortunately it was left in place, or I would
never have known of its existence.  It was omitted on later models.
It is a wonderful feature and give the piano a punch that other
uprights don't have.  It opens both theme valves at a preset theme
level.  This just clears out a few folds in the expression box and lets
more vacuum through.

Someone in the future might have the same thoughts about your softening
device.  There may actually be a roll somewhere that sounds better with
it on.

Spencer Chase