In Automatic Music Digest 95.09.05¶
Richard Huggins <rhuggins@rapidramp.com> wrote:

>    The Yamaha Diskclaiver II system is MIDI-compatible. I'm not sure if
> the Pianodisc system is. The latter can be retrofitted, I believe, while
> the former must be installed as the piano is built.

Yes the PianoDisc system is MIDI in and out.  It plays its own disk format
as well as Disklavier format.

> I've seen a demo of
> the Disklavier II and it not only reproduces the performance (with all
> parts moving) but will also play a MIDI tone generator and thus draw
> from it added stuff, such as drums, brass, etc.

PianoDisc also can be purchased with built-in synthesizers, but unfortunately
they are not the same channel arrangement as Disklavier.  The original
PianoDisk has a Proteus EMU-1 chip (that's the one I have).  The newer ones
are Proteus chips rechanneled to General Midi.

> Pre-recorded disks can
> be bought and the piano (or other tracks) can be turned off to allow
> playing along with the other accompaniment. I've also been told that the
> disk can be edited within a MIDI sequencing program, meaning that the
> performance can be altered and/or improved (wrong notes corrected, notes
> added, timing fixed, many other things) and then reinserted into the
> Diskclavier player for playback on the piano itself. Sort of the best of
> both worlds.

Many places (such as Invisible Touch Music) will sell music in either format
(or as .MID files, or General Midi)