DS8 hasn't read this series yet, but he has similar interests and I thought it looked good.

http://www.amazon.com/dp/006207041X...&colid=3KXX4Q1ZYSJAJ&coliid=IPABIIRPA5JG

Other than that I don't know what to say because he is obsessed with history. He did read "The Unicorn Chronicles" last year and enjoyed that series. (it sounds girly but it's really not).