I like Max, but it's a lot more common than what I usually go for. I'm looking for some classy, but no pretentious, middle names! Vintage etc.
All I can think of are..
What about: Sebastian, Atticus, Alaric, Cassidy, Amadeus, Abraham, Alexander, Elias, Elyan, Elijah, Finnegan / Finnigan, Jeremiah, Zachariah, Tobias, Tennyson, Alberto? I also noticed that in your signiture you have Sylvester and Percival, I think they would go nicely with Max too :)
Max Sullivan, Max Ambrose or Max Solomon.