Hi NASAMike,
I'm not sure I understood your question correctly ...
• If you want to ADD additional parts (channels) to a existing MIDI song, you have to specify the part assignment for the channel to be recorded. Please refer to the chapter "Recording Each Channel Individually (Multi Track Recording)" in S970 Owner's Manual (page 69, step 3).
• If you want to change the Voice of a Part in an existing MIDI song, simply press [Mixing Console] button until "Mixing Console (Song)" is displayed. (You can toggle between Channels 1 - 8 and 9 - 16 by pressing [A] button). Then press [C] or [H] button to select the "Voice". Press one of the "upper" buttons 1 - 8 to call up the Voice Selection display and select another Voice there.
Then SAVE your changes to the MIDI song:
• Go to "Voice Creator" and there to "Setup" tab.
• Press SONG [STOP] button to go to the beginning to the MIDI song.
• Make sure to have ticked the FIRST SEVEN (7) check boxes in Setup tab (Voice to EQ), but NOT have ticked the LOWER FIVE (5) boxes (Keyboard Voice to Guide Setting).
• Press "APPLY" ([5] button)
• Press "SAVE" ([ I ] button). Change the filename to prevent the original file from overwriting. Finally press OK to save the new file.
Hope this helps!
Best regards,
Chris