One of my sons plays Tau (the other three play Tyranids, Orks, and Imperial Guard, respectively). My Tau-playing son has the older version of the Codex, not the one that has the XV-95 and the Stormsurge in it. Are these two included in the Mont'Ka book (which as I understand it also includes some scenarios and whatnot involving the Imperial Guard)? Or do I need to buy just the new Codex, or must I purchase Kauyon in order to get the rules for the XV-95?

It's kind of an issue, because I want to get him an XV-95, but don't know which of the codex or the supplements to get to go with it.

Thank you for your help.