Apparently, according to Wookieepedia, Sifo Dias deliberately sounded close to Sidious and would later be revealed as the same (in Ep III). Of course there were far too many loose ends left for ROTS, so that plot thread ended up neglected, and it's my biggest pet peeve. A novel or comic (can't remember which at the moment) was later created simply to answer this question, and it was just some lame-o new guy who really was named Sifo Dias. I truly wish that plot thread hadn't left the entire AOTC tapestry so threadbare. When I do find a set of PT edits that may be my definitive versions (thus far I'm simply open to variants of the tale), it will certainly have no such reference.

As for ben_danger's belief that there should be an obvious villain (something which struck me as odd when I first heard about it, but now is making sense to me), there is an interesting edit in the works, though currently on pause, that seems like it might remedy this situation quite nicely: Episode II: Army of the Republic.

It seems like it could remedy the problem nicely, and his episode I edit looks promising and I'm currently downloading it and hoping to give it a go when this semester is done.