Having had problems already with Sonos speakers (you can't output sound directly to them from the laptop) and with two hi-fi speakers in my stereo system doing nothing, it made more sense to me to see if they could be hooked up. The focusrite is hooked up through the stereo amplifier. The speakers don't have self power and I think this is the reason the volume has to be increased to about 75% on both the focusrite and the amplifier to approximate real instruments. But I'm happy with the result so far.
Aye,
Genghis
I'm not arguing with the solution. I used to do that myself until I discovered that my stereo amplifier has bluetooth capability. But, I don't understand why you can't output directly from your laptop to the Sonos speakers. They're bluetooth, aren't they? I've got a similar Bose Soundcloud II speaker and use it the same way for exactly the same purpose.