Answered my own question, as I hadn;t read Metallica's statement:
"This year we are super psyched to have the Red Hot Chili Peppers join us to close the main Orion stage one night while we hit that stage the other."
04/03: The Acacia Strain(?)
05/13: Slipknot/ Hatebreed (?)
05/26: Metal Alliance (?)
06/05: Aborted (?)