I am doing a similar thing however I have previously passed the IREX albeit many years ago.
The IREX exam is significantly more difficult than the FAA exam. I studied on my own for the IREX from what was then a loose leaf publication (dont recall the author but I probably have the book somewhere). I am about to purchase a new book for the conversion, I reckon between the FAA stuff and the CAA/CASA I must be near a world record for number of flying books!
From what I have been reading on pprune recently there seems quite a few of us doing FAA to CASA around this time.