I do not have any experience with the iPod-fitted PianoDisc but I can
offer some guesses.  The iPod can play a few different file formats,
and I have no idea what PianoDisc provides but I would guess that
the connection from the iPod to the PianoDisc is via the audio output
and that the PD receives audio encoded MIDI through its audio input
connection.  This has been an option for the use of standard CD players
for some time.

If this is the case then it should be possible to convert the MIDI
files to WAV with Mark Fontana's Mid2PianoCD program and then convert
these to MP3.  It should then be possible to upload the audio to the iPod
and play them on the PianoDisc system.

I am currently working on an on-line service for providing such files.
Initially, I will just provide CDs for use with the four major solenoid
players as a test of the viability of this marketing technique.  Songs
may be selected from my library of 4330 piano roll emulations.  I am
almost ready to go on-line with the system and hope to add the ability
to electronically transfer MP3 files soon.

If you would like to take part in initial testing of the site or want
to experiment with MP3 files (using the iPod or otherwise) contact me
by email.

Best regards,
Spencer Chase