To check whether Internet Streams work properly as well, I tested an MP3 160kbps stream and two AAC+ streams (32kbps and 96kbps). MP3 works nicely, but the Hifiberry stays quiet with the AAC+ streams (on the analogue output all streams are played). Also, the playing time in XMBC is running normally, while the streams are inaudible. So it _seems_ that the Hifiberry might have a software problem (are there any format limitations on that part of the string of components?). I should note that AAC files (in this case .m4a) are played normally.
In any event: Everything that is played is of very nice quality! Thanks a lot for this!!
AAC+ Stream(s) do not play on Hifiberry