I suggest editing out a chunk of the Emperor's dialogue. As presented in ROTJ, he's a very stock villain. When you imagine him sitting there, most the time silent, you can feel the tension building up. So when he does speak, his words could that much more weight. I also suggest having him speak more slowly and collectively, as the character did in Empire Strikes Back.
Silence among contrasting characters, when done correctly, is a superb way of creating a foreboding tension. The way it is in ROTJ now, is very scripted and watered down.
Consider this.