Hi to all!  This is a very challenging thing to take on, adding
expression or modifying musical arrangements using something other
than a musician's expertise!  I speak a bit from experience.

Some years ago I built a pneumatic roll recorder with an 88-note
tracker bar, and added a 'keyboard' that has the Ampico expression
encoding directly available by keystroke (three buttons for intensity,
one for fast crescendo, a toggle for slow crescendo, and a cancel
button).  Two opposing keyboard layouts are for treble and bass.

This setup allows me to play back an 88-note roll and add real-time
expression to it, all played back on my Marshall & Wendell Ampico
(fitted with Spencer Chase's e-valves) in real time.  I had this
recording apparatus in the hospitality room at the AMICA Chicago
Convention.

This setup all works great from a technical standpoint, and I used
it in an attempt to 'improve' some favorite 88-note rolls.  To date,
I can't say that I have improved any of those rolls -- the original
arrangement is far more important than anything an 'old computer nerd'
can add.  In other words, I need to hire a musician if I want music
to be arranged.

This whole problem became more apparent when I installed one of
Spencer's e-valve systems in my now-restored Wurlitzer B orchestrion.
With MIDI files there is a lot of music that will exercise the
instrument in a way that old rolls can't.  Wurlitzer 125 and 150 band
organ MIDI files (downloaded from Terry Smyth's web site) sound great.
They don't use the range of the instrument but they have percussion.

I have played a number of other arrangements on the instrument,
including nickelodeon 'A' rolls, Duo-Art, Ampico, etc.  The thing
missing on these is the percussion.  How do I add bass and snare drum?
This seems like it should be easy, but it isn't!  The timing has to be
perfect for the bass drum to sound decent.  I'm convinced that it will
take a musician to add the snare drum part; it is part of the musical
arrangement.

The bottom line of all of this, from my perspective, is that computer
programs can not yet arrange music, and this is what we seem to asking
for.  At best, they may be able to change formats, but to what end
result?  That is the challenge.

In the meantime, I'll spend hours editing MIDI files to get the bass
drum to beat when it needs to, down to the last few milliseconds --
it makes a difference.  Hmmm, now to find a drummer to add the snare...

Larry Emmons