So it was annoucned that you could now link Sonos to your SoundCloud account. But there was no explaination on how to do this as it did not appear in the list of supported services like Google Play etc. After a quick but of searching on their support site, it turns out that you go to the following location to add and then approve via your browser
Sonos App or Mobile App > Add Music Service > Sonos Labs (hidden down the bottom) then select SoundCloud.
Enjoy some great music.