Read the Detailing 101 thread. It says if you wish you may apply a wax after applying a few layers of Klasse. It's mainly just for appearances though, to get that warm and deep look. There are a few warnings though, 'cause you may get a little ghosting or hazing.
Apparently most people will apply a wax after a few coats of Klasse to get that little extra "WoW" look. Once I do finish applying my 3-4 coats of Klasse I'll be applying a layer of wax.
Also, if you do use a wax make sure you don't use a cleaner wax as it will strip away the sealant (Klasse).
I really recommend reading the Detailing 101 Thread. The guy seems to know what he's doing.
More-so then myself.