I have read most of "Java RMI" by William Grosso and it was helpful. He covers how to design an RMI interface in depth. (For the exam, Sun tells you what the interface is supposed to be, but it's still interesting an interesting topic.) He also has at least one very nice example of a pool class where you would want to implement it with multiple threads. For example, he shows how you how and why you would use a separate thread for updating the pool... actually he creates several threads.
The Max is also good because there are practical things that are demonstrated in that book that seem directly related to the exam, for example how to programmatically start up the RMI registry (without using the "rmiregistry" command from the command line). Grosso sort of covers this but not in a way that would be easy to find unless you were really looking for it. Max talks about a database object design which could be used either in network mode or in standalone mode. Overall, I feel like the Max book gives more of a surface treatment of each of its topics, which is only to be expected, it is a relatively small book and it covers threading, RMI, the GUI, logging and a couple of other topics too. For some of these topics, a surface treatment is all that is needed, and the book discusses specific things which are very useful to know for the exam. But there are topics that require more depth unless you are experienced, and that is where you will need to look for particular books or other reference material.