I found a simple "solution" at least for the next time:
I have plugged a male / male audio cable from microphone to headphone in all my clients. Then I read the local microphone stream and, what a miracle, i can visualize what Im hearing.
Not a good solution, but it`s doing the job..
One Question: Is it possible to re-grab the destination as a stream in javascript? Then I would not need the audio cables..