Best tutor: yourself and the AIP - it is definitive.
If you've got your CPL subjects, IREX is just IFR rules and some revision. (If not, there will be a bit of brushing-up on MET, planning etc).
IFR rules are actually quite logical; made harder by the way CASA write and the way some people think. If you KNOW you will be safe (safe altitude, sufficient fuel, etc) then you can probably do whatever; if you can't be SURE you are safe, you can't do it.