In my opinion, Joruus C'baoth should not sound anything at all like the Emperor. He's a very different character, and much younger than the Emperor was at the time of his death. Joruus is described as slightly past his middle age, if memory serves me right, and in excellent physical condition. His voice should not sound very old, nor creaky like the Emperor's, IMO. A deep, slow and imposing voice, something similar to Saruman in the LotR films would work very well, I believe, but with a crazy edge to it. Don't think I can pull it off myself exactly, though. Maybe the Galactic Conquest people would have some ideas?