I agree with (and enjoyed) Craig Brougher's comments about the solenoid
pianos.  I have a QRS Pianomation (or, at least, I used to) and I have
done a great deal of experimenting with it.

First of all, the leverage and points of engagement on the piano action
has to be ideal, and in an upright piano, it is _not_ under the keys,
as QRS (and other makers) suggest that the unit be installed.  Say what
you will, but the upright piano simply is not designed to be driven by
a player action from underneath the key-backs.

In a piano with short keys, or with the center point located too far
toward the keytops, the key will have the nasty little habit of riding
up the center pins, soon wearing the hole in the key out.  (Some people
call that condition "pully keys".)  This also wastes power that should
be available for playing the piano.  So, I built a "stack" with levers
for the solenoid rail and it made a big difference.  Also, the solenoid
position was very critical even at that, so that tells me the system is
marginal, even for a 52" Foster upright piano.

I have my doubts, though, of this system even coming close to playing a
concert grand at it's top power, unless more powerful solenoids are
used.  Also, the power curve of a solenoid is completely different from
a pneumatic.  In a pneumatic system, the more the striker pneumatic
(span) is open, the more power it will have as it operates (in most
cases).  Conversely, a solenoid will reach its power peak when the
plunger is parallel with the field coil, at about two thirds of its
stroke.  This is almost the opposite effect from its pneumatic
counterpart, so by simple physics these are different animals.

Actually I agree with Craig that pneumatics are more suited to the
task, especially in the larger grands.  But installed in a manner where
the solenoids have the proper ratio, in the smaller pianos, there
shouldn't be much difference, if any, in the arrangement.  To enable a
solenoid piano to play anywhere close to a pneumatic piano, the
solenoid _must_ be able to throw the plunger full stroke, which is far
greater than the average key-back travel.  While this would not be an
issue in a pneumatic unit, it's critical in the solenoid piano.

In layman's terms, the solenoid must be able to throw the plunger full
stroke, and have the proper travel for the action, plus just a little
aftertouch.  If not, the hammers will not check in soft playing.

Musically
Andy Taylor