What kind of Onyx is it? What does it look like? Onyx's have been around since 93, so it could be pretty old. I used to own one so I know quite a bit about them.
Start it up and type "gfxinfo" and "hinv" in the shell and give us the results here. Maya comes with two MR licenses and I think it can thread up to two processors.
Yes Irix can read windows formated cd's but it may truncate the names depending on how you burned it. In nero if you choose and iso9660 version 2 you with joliet names unchecked. With those options irix can read up to 31 character file names without truncating them