No...
I would not use a 5.1 receiver, simply no reason. First off, there is no need for a tuner since the Sonos will stream radio stations. Secondly, you won't want to have competing variable volumes, this can only lead to disaster. I would use a large multi-channel amplifier such as a Speakercraft or Russound like the BB1235 from Speakercraft. Use sonos as your source and never have to worry about anything again. I use this in installs quite frequently and it is simple and easy to use, but most importantly very reliable. My 2c.