To Unlock Everything:
Just beat the game and save the info to your memory card then go to bonus materials to see them. Don't worry about finding the tomes, they are all opened when you beat the game.
Kain's tomes - found throughout Kain's journey
Making of LOK Defiance - finish game and save to memory card
Raziel's tomes - found throughout Raziel's journey
Soul Reaver 1 - opening start new game
Soul Reaver 2 - opening start new game
Switching Reaver Alignment:
If you switch alignments while holding down the square button when your reaver energy is full, you can sucessfully change which spell you use without losing your full bar.
The Tube Reaver:
While the game is paused enter the following:
Up, Down, Left, Right, R2, L2, Triangle, Down, and Circle
You'll know the code will have worked when Kain says, "Fear the Tube" It will allow you to wield the mighty tube reaver.