Some time ago I spent a deal of time trying to play directly from my iPlayer web page to the Sonos speakers.
All threads on this topic seem to sink to a kind of blame game between Sonos 'fanboyz' and customers who just want to be able to use a speaker.
I still cannot see why the Sonos controller can't just stream whatever you are playing on your desktop because, for example, BBC iPlayer on screen has many more features than most streaming services and hence a desktop version of 'play direct from this device' would be really useful.
Having added an Alexa enabled device, (A Sonos One) all I have to do to use player over the Sonos is to link the Sonos 1 to whatever speakers I require to play and then on the OSX desktop I can see The Sonos one listed as an output device from the speaker icon at the top of the screen. Click on that and bingo, everything works as it should.
This means I can browse the BBC schedules, play stuff that is only available in the UK, play podcasts that I can't see in through the Sonos Apps (for some reason), skip back and forth in the current programme and loads of other stuff that Sonos just won't do. Well done Apple I say. Why Sonos could not do this years ago I have no idea.