Fran,
I called Roland today and I'm not sure I got the final answer to your harmonizer questions. My good source is still on vacation and so I spoke with a keyboard tech support guy. He seems to think that the internal vocal harmonizer can only see which ever one track you select to have the vocal harmonizer read and not be able to see incoming midi messages from an external source. However, I'm not sure he truly understood what I was asking, because I'm not sure I understood myself. Please call and talk to Jan Vogul at Roland maybe at the end of the week. He is the one man there that really knows the arranger products in tech support. If you need their phone number I can give it to you.
George Kaye
Kaye's Music Scene
Reseda, California