sw mixer & spotify

I’m new to Volumio and using a Raspi2, HifiBerry-Digi+, Volumio 20161212. USB flacs & my spotify tracks work when mixertype=none, but because I have hifiberry Digi+ into classD amp I want to use sw mixer. When selected I have no problem with USB files but sadly no output from Spotify. What to change to fix this ? in /etc/spodp.conf output_type=hw:softvolume, is this correct ?