The half-second delay in the Disklavier can be turned off, but there
will still be a delay that depends on the MIDI data being sent and the
DKV's response time.  I have a MKII DKV, and the 500ms delay is turned
off at the main control box.  I also have a DSR1 fitted to the
instrument, but this does not control the MIDI delay.

According to the manual, you press the Func/Edit button on the main
control box to access the MIDI setup functions.  Select MIDI IN, and
rotate the volume control until the display shows MIDI IN = Realtime.
I have not tried this, as I prefer to have a known delay time instead
of a random one.  I recently wanted to synchronise an organ sound track
with a superimposed MIDI track for the piano, and found the best way
was to leave the 500ms delay intact, and to start the piano 500ms
earlier than the sound track.  Tricky but it worked.

Peter Phillips
Sydney, Australia