Hi Hornox,
sndconfig should definitely play a sound ("Hello, this is ..."), when it is configured correctly. Does it detect a sound card?
I just tried it to play a MP3 with my production server and I got the same error as you.
On my test server, where the sample works, I investigated a bit more and found that I forgot to include a "-o alsa" to tell mpg321, which output it should use. Try also some other values for "-g volume":
mpg321 -g 75 -o alsa file.mp3