Will it run out-of-the-box on a RPI B+?

Are you setting output = i2s or output = hifiberry_dacplus ? You must set it to output = hifiberry_dacplus as per the comments in settings.ini. If you are setting it correctly then please try the very latest version (http://www.woutervanwijk.nl/pimusicbox/musicbox0.5.1rc2.zip) and provide the output of

  • lsmod
  • cat /sys/class/sound/card*/device/modalias
  • aplay -l
  • cat /etc/asound.conf
  • cat /etc/modules
  • cat /etc/modprobe.d/blacklist.conf