I think I know your problem. Most of these games hide their data when you use an ISO extractor/mounter , so you have to dig in the ISO to get it. I remember Kingdom Hearts and Chrono Cross using this format from what i looked at them.
EDIT: also yeah IRX and IMG sre pretty much useless for data ripping, theyre just code.
EDIT: also yeah IRX and IMG sre pretty much useless for data ripping, theyre just code.