It depends on the streaming service - the Spotify app sees Sonos speakers and lists them as targets to which the music may be transferred by selecting these. The Amazon music app also shows Sonos speakers as targets you can choose to play the music from.

I use my S1 app only to play music from my NAS.

Thanks Kumar, but I can’t see the sonos speakers available in my music apps (Spotify or Amazon). 

I have a Connect Amp that’s installed in the house. The system’s about 10 years old so I’be been blaming that for the non-user friendliness, but I won’t to make sure I’m not missing any tricks!

If you think I should still be able to find the speakers/amp in Amazon, could you let me know where? 
 

I use Spotify, although I do have Amazon music as well, I don’t use it much. This below suggests the answer for Amazon Music.

For Spotify, clicking on the speaker icon at the bottom left of the now playing screen brings up the list of speakers, that includes Sonos speakers that the app has discovered.

 This is what the speaker list looks like on Spotify.  
 

Thanks very much Kumar and MoPac. I’ve given up on Amazon Music - I couldn’t get it to work. I’ve reinstalled Spotify and it’s working - I can connect it to my Sonos amps/speakers and play music using my Spotify app. 
 

Thanks again, really appreciate your time.