no sound - Pi 3 - Altec Lansing XT1 USB

Installed Volumio on the new Pi 3. Analog output works. USB does not work. Strange enough RuneAudio detected the Altec XT1 immediately incl. the correct name. They also work perfectly on my Mac.

Any idea what to do? Volume only offers Hifiberry options for output.

Sorry, I am not the digital expert.

Thank you in advance!