Did some more comparison with my other equipment. I am sorry to say that the sound quality is a bit poor. I can only connect over MP3 with the Xtreamer and I have to say this is not really seamless. I have to connect manually to get this thing to work.
I will stick to streaming over Bluetooth or via my Apple TV. For Windows I have to trust to the good old audio cable (except for iTunes which does stream to the Apple TV).