S770-Record to available track in a song with voice of another digital piano

[huong9999]

I have a song that I created in my PSRS770. I would like to add a piano track to an available track in the song, but using another digital piano voice instead of the piano voice that come with my keyboard. Is this possible? How do I connect the two together to do this? The other piano is a stage piano P200.  Thanks in advance.