Streaming Sound via Airtunes (AirportExpress)

While using Airtunes via iTunes I messed around with the problem to stream the system sound to the AirportExpress (e.g. Youtube Music).
After looking through some forums I stumbled over a little tool called "Airfoil".

After installing it I can choose the AirportExpress as the output speaker for my system sound:

Now all system sounds are streamed to the AirportExpress and it's possible to play sound of youtube videos directly to the AirportExpress. The sound is a little bit delayed (so using it as movie sound stream is senthless).