How to set streaming quality through Sonos?

[suespotify]

I use Sonos for listening to music and just signed up for Spotify Premium. When I listen to Spotify music through Sonos it is using nearly all of my [pathetic] 2Mbps DSL connection. Is there a setting for the streaming quality of Spotify+Sonos? I want to set the quality to "normal".

BTW: I asked this question of Sonos support and they said to ask Spotify support.