When a playlist includes a song that I already have in iTunes, I get a message saying that the song can't be played. It won't stream the song from Spotify or play the local version from iTunes. I have tried changing the settings for playing local files; the result is the same whether I enable or disable the options for playing each type of local file.
These are all songs to which Spotify has streaming rights, as far as I know.
For the sake of simplicity, I would prefer that all the songs just stream through Spotify without iTunes being involved at all. My second choice would be to switch back and forth from streaming to local files. So far, neither option works. How can I get those songs to play when I am streaming Spotify?