The Budapest Defense

I have been having trouble in my encounters with the Budapest.  I know the main lines well enough, but I can't grasp the theory behind them as it is too bizarre.  Can someone who knows this opening well post some of the theory behind the lines?  The reason I am asking this is because even though I have acceptable knowledge of the lines, I can't punish my opponent for going out of book too early if I don't understand what's behind the moves of the opening, instead of just the moves themselves.  If you post on this, thank you for your help :)

le livre le plus complet et le plus instructif est celui de Viktor Moskalenko (2558)

You can join this group, lots of vote chess games in different lines, very instructive

http://www.chess.com/groups/home/budapest-gambiteers