In other news, I've (at long last) solved my issues with Spotify, which is now working perfectly!!
The problem was that instead of using the proper Spotify website to set up a starred playlist, I was accessing Spotify, via the webpage/player, and it wasn't 'talking' to Volumio. Therefore, when I was setting up a playlist there, it wasn't going anywhere other than the webpage/player.
Setting up playlists on the proper Spotify website, however, has solved the issue, and now all the playlists I've set up there appear for selection (and playback) on Volumio. Job done!
Tomorrow I shall pop my other SD card into the RPi, loaded with Rune Audio (and my library of music), and see how that compares with Volumio. I certainly like how, with the latter, you can see the album art and search music via genre, not just artist. Some also say that Rune sounds better than Volumio, so we shall see!
Marco.