Hi,
Notation Player is designed to be mainly a player for .not files that others have created using Notation Musician or Notation Composer, similar to the way that Adobe Acrobat Reader only reads files created with other programs. As such, it has limited capabilities - the volume levels between staves (tracks) cannot be changed, but you can control the overall volume using the volume slider on the main toolbar.
If you want to edit .mid files for sheet music (and some sound leveling), you can try out Notation Musician (
www.notation.com/NotationMusician.php).
If you want to edit both the sheet music and finely edit the performance, you can try out Notation Composer (
www.notation.com/NotationComposer.php) It's really a hybrid notation/sequencer application, done in a way that's more friendly toward everyday musicians.
If you have any further questions, please do ask away
ttfn,
Sherry