One of those other voices could always be given some expository dialogue.
“I am the voice of Darth Bane, the first Sith to go into hiding a millennia ago and plan our revenge. I and all my successors now reside within the vessel of the final Sith Lord. Don’t fuck with us!”
Wait, wrong thread.
Seems like the perfect song premise for the The Rise of Skywalker: The Musical
It’s almost like before his “death” his identity was pretty contained to the man “Sheev Palpatine”, but after his “death”, the collective consciousness speaks through the shell of Palpatine.
This was how I assumed things to be on my first viewing in the theatre; that it was Palpatine’s actual corpse being reanimated by some kind of amalgamated essence of evil. Dooku and Bane have canon voices that could be imitated (as do Vader and Maul though they arguably weren’t Sith when they died). I like this idea a lot since it adds a greater finality to the conflict rather than being just Palpatine again.
Techincally Dooku wouldn’t be one of the voices. Since he never killed Palpatine, the spirit never passed into him. Someone could impersonate Hamill’s depiction of Darth Bane in The Clone Wars, though. One voice could techincally be Plagueis, but we never heard his voice in canon.