Ferret,
I self studied Law, HF, and Met and had the Nathan Higgins self-study books for Systems and Nav. I did them all up here in Darwin in four months, while working full-time. All were very easy to do self-study
If I'd have known how easy the Systems and Nav were going to be, I'd have got the AFT self-study books for Flight planning and Performance and Loading. As it is, I'm heading off to Maroochydore tomorrow to do the last two. Should both be easy
Before you do the ATPL's, I'm pretty certain that you've got to do your IREX (I may be wrong here, others may confirm this?). For IREX, I'd recommend Bob Tait's IREX book. Very informative, easy to follow, and well set out.
Hope that helps.
DIVOSH!