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. 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. 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.

---Richard¶
Richard Huggins, Tyler, Texas, USA¶
rhuggins@rapidramp.com