Well I believe that it's Tie-dus. It just seems more natural for me and all my friends who play pronounce it like that.
I'm also Australian and until you've met every single Australian who has played FFX you can't say that Aussies mainly pronounce it Tie-dus or Tee-dus.
Also may I just add, just because James Arnold Taylor pronounced it Tee-dus doesn't mean that it IS Tee-dus.