It's hard to focus on a moving target and "Paged" feels more natural to me since that is how sheet music works. It allows you to look ahead without worrying about the upcoming notes moving.
Since an individual can only play one part at a time, rather than showing two scrolling parts, two pages of the same part should be shown. Initially, page 1 can be shown above page 2. The playhead is the only thing that moves, from the left of the screen to the right. Initially it moves across page 1. When it reaches the right side of the screen, it moves to the start of page 2, below and to the left. At that time, page 1 is replaced with page 3. This way the pages remain still, while allowing the user to progress through the song.