The Eye of Terror is to Chaos as is Terra to the Imperium. The Black Crusade does a good job of detailing Chaos forces, but an RPG book solely around the EoT would be crazy, literally. The EoT is host to innumerable amounts of daemons, warpfused fauna, all sorts of unique daemon worlds, dark mechanicum forges, daemon princes, pseudo-daemons, and all other manner of Chaos-y goodness. Why settle for the Screaming Vortex when the Eye of Terror is as close as you can possibly get to the Chaos Gods. shit's crazy yo
The fact is Black Crusade is a tabletop roleplaying game. If you want play in Eye of Terror, just talk to your GM and start making stuff up.