I have installed a couple of MIDI interfaces into pneumatic players in
the past year.  I work for the Wicks Organ Co. so naturally I used some
of their direct electric chest magnets [direct action magnetic valve].

I used the smallest ones they make, which have a 5/8" valve attached.
These magnets are lightning fast and do not get hot.  They are also
very rugged in construction and easy to work with.  They are $7.12 each
from Wicks.

I mounted them to a length of poplar wood, sized 2.5" x 1.25" x the
inside width of the piano case.  A hole is drilled through for each
unit to accept a straight length of brass tubing to connect a tracker
bar tube to.  Depending on the piano I mounted that on top of, or just
behind, the spool box and then teed into the tracker bar tubing.

For the MIDI boards I used the Octet UM1, which is now being made by
MIDIator, with a special high current driver board which I designed
specifically for plugging into the UM1 or UM0 boards.  It is capable
of driving the heavier load of the Wicks magnets and is easier to wire
to than the ribbon cable terminators that come with the UMx boards.
(I would be glad to supply them to anyone who is interested.)

And of course a power supply is required.  Radio Shack makes a 25
ampere switcher type power supply which is small, light, and relatively
silent.  This setup should run you somewhere around $1200 in parts.

This setup works very well for me and has attained faster repetition
than most rolls I have allow.  It is quite something to watch that
pneumatic player fly through some of the more complex MIDI files
available.  I would be happy to answer any questions that anyone has.

Thank you,

Allen Moe - Moe Piano & Organ Co.
Highland, IL  USA
http://www.mpoc.50megs.com/