The front/back movement is typical for suspension forks in general: by definition there is a certain amount of play between the stanchions and the lower legs. Try this out on a lighter fork like a Rock Shox SID and you'd almost be frightened about the movement. In practice you don't notice this and the DJ takes big hits smoothly in our experience. Please try it out first and fiddle with the air pressure before you start changing springs. These changes can quite easily be done at home, check the manual for details. There is also another way of influencing a fork's behaviour which is through a lighter/heavier-weight oil.
Perhaps it's wise to search the Web for clues on this - there are so many enthousiasts out there who have already "beaten the path" for you Also, Usenet discussion groups like rec.bicycles.tech might prove useful.