Best books to prep for SANS 502, 503 and 504?

Good Day all, I am finally transitioning out of the Military and already accepted employment in the Civilian sector. I will primarily be doing Network Intrusion Prevention/Detection, Incident Response, Defense against attacks such as ddos, etc...I have the ability to attend SANS 502, 503 and 504 training, and would like to complete all 3 by this time next year.I understand that you cannot get a hold of the SANS material unless you take the class, which is fine, but I would like to better prepare myself before I take the courses. Can anyone recommend some books that might be helpful to read before getting involved with these courses? I have a good level of technical networking and information security knowledge already, so the reading material should be easy for me to digest. Thanks again for the assistance!