Hi Jimny,
Yup it appears a minefield but I got through it to do my ATPL's (JAR to CASA) and there is one name to sort it all out for you (no affiliation btw) AFT. They have the best comprehensive texts and online practice tests. But use Bob Tait for the IREX without a shadow of a doubt.
You will need the whole set of books to become acquainted with how the rule structure is set out.
Good luck
Si