My goal was to stream all sounds no matter what source and the solution was simpler than i thought.
What you will need:
A VideoPlayer which allows you to modify the audio sync, like VLC.
Download Soundflower (if you are using Snow Leopard just install it) extract it, open a terminal and run
$ cd /sound_flower_lion_1.5.3/Tools $ ./build.rb --dep
Restart your mac, open "System Settings" "Audio" and change the default Output to "Soundflower (2ch)".
Since the AirPlay protokoll has a 2seconds delay by design you need to change the audio synch if you wanna play videos and stream the sound to a wireless speaker.
In VLC for example you can modify the audio synch with the keys "f" and "g". Set a delay of -2000ms and video and audio will be in sync.