Well, the whole thing of reading/preparing in advance doesn't really make a lot of sense in my opinion. Mostly because the question database (exam questions) put the emphasis on areas which are poorly covered in the textbooks or aren't even covered at all. I rarely used the textbooks during my studies because of this very reason. And secondly, due to the sheer volume of all the different subjects, after reading half way through the books you'll notice that you can hardly recall what the previous books where about, especially the details which the CQDB (exam questions) is mostly about. What I'd recommend to get and what helped me a lot during my studies, was the Oxford ATP DVDs. Available also as an on-line course, which is roughly half the pierce of the DVD course. See link bleow.
ATPL