as for the .pak, you have to extract the data using a tool. I’m not 100% sure what tool, but maybe this (http://sourceforge.net/projects/dragonunpacker/) would work?
there are many different stream file formats for the PS2, but since they’re compressed within the .pak file, I can’t tell you which one it’s using (although it doesn’t matter really, since VGMstream can play basically all of them)
i’m not so knowledgeable on data extraction within archives, but if anybody would know, it would be the members over at hcs64.com (http://hcs64.com/mboard/forumlong.php).