We just spent 4 days in Munich and used Rick's 2015 Germany guidebook. For train travel questions Rick suggested using EurAide in the hauptbahnhof. All of our train, U bahn, and miscellaneous questions were answered by Alan Wissenburg and his staff. Alan has a world of patience and a wonderful sense of humor answering questions from travelers. Just watching him interacting with travelers is astounding. He is so knowledgeable and directs travelers to the best destinations using the most economical train itinerary. We dealt mostly with Alan, but his staff is just as hard working. I usually don't give kudos online, but I felt that he and his staff deserve some positive feedback because of their professionalism, dedication, and great humor dealing with us novice travelers. If you're in Munich, have EurAide, Alan, and his staff answer your questions.
With EurAide , you can get reservation that are required with a railpass from here, before you go. Many times you can't get the reservations at all, or, if RailEurope sells them, they are more expensive than from EurAide (note: RailEurope marks up the reservations they sell. EurAide sells them for the same price you would pay over there, but there is a substantial fee for the service. EurAide is cheaper if you are buying a lot of reservations.)
However, if you are just buying train tickets over there, I think your best bet is to deal directly with German Rail at the Reise Zentrum.