The Emperor that Revan faced in the Revan novel was not a Voice but was in fact his true body. After the attack the Emperor created the Voice in order to protect himself from future attacks. This also proves that the Emperor is in fact a Sith pureblood

2 previously unmentioned Dark Council seats and members including the Keeper of Mysteries to which the description is unsurprisingly vague

The Republic are winning the war, this isn't really brand new info but clarification on how the war is swinging, however key to the Empire's victory is close at hand.

Darth Marr is the leader of the Dark Council, not the official one but de facto. He is the most powerful member.