I once had a Seeburg MO piano organ.  When the piano was to be shut
off, there was a hammer rail lift, similar to soft pedal.  However,
this one lifted the hammers all the way to the strings.  Therefore
the hammers could not play at all, when organ only was required.

It would seem to me that this method of silencing the piano during
solo instrument passages would be much easier that installing felt
mufflers, or stack cut-out blocks, which would interfere with the solo
instruments which are dependent upon the pneumatic stack.

Bruce Clark