But sadly the Android WifiP2P world is damn complicated and we did not manage to archive our goals.
The devices connect over the WifiP2P interfaces and connect into their own network. Sometimes they are able to transmit messages and also the audio stream is ready to go.
This very case is not well documented and we had to dig through all sorts of documentation and stack overflow questions, but in the end only trial and error helped us.
We had a lot fun playing around with Android, because for most of us, it was our first Android project. It's kind of a cool to realise that you work on a topic only few people worked on before...that feeling helps us through the hard hours of documentation reading.