I gather my info from the internetz, and games I've played.
I've listened to the TOR: Revan audiobook, and read a few chapters of a book where Ben Skywalker found Obi-Wan's lightsaber, but that's about it, nothing more
I've beaten all the Battlefront games, played TOR, and have beaten Jedi Academy, and KOTOR I and II.
I go with the duo. I don't think Sidious, any Sidious, is far enough above his peers to be able to take on two powerful sith lords and win, and these are two of the stronger.
The main difference of Dark Empire Sidious isn't his personal power, after all, it's his big techniques, and he's not going to have much time to do them.