Disklavier

I picked up a DKC850 at the local Yamaha dealer yesterday, he said to try
it, if it works and I like it, then come back in a few days and pay for it,
or return it. Sounded like a great deal so I went for it. 

 

He said that instead of re-wiring the whole piano, what would be easiest
would be to plug the  850 into the MIDI-IN port on the existing DKC100R,
then just use the 100R as a pass-through device, and all should work fine,
and I could unplug the MU50 because the 850 will duplicate what the MU50
does and do it better.

 

Followed those instructions, got it working, kind of.  It played about 75%
of a song from the 850 then the sound just stopped, no error message, and
per the 850 display, it was still playing? I also get a humming out of the
Pioneer speakers mounted on the bottom of the piano that was never there
before.

 

Also, there was no way I could get it to have anything other than the piano
-- no drums, strings, bass, nothing.

 

Suggestions?