Cannot play my music on Sonos after deleting Spotify

Both things should not be related. Can you elaborate on your question? Why did you remove Spotify? Is TuneIn still listed as a music service on your system? Did you try to add it?

Where are the iTunes music stored? Not sure TuneIn is related, more likely either setting up a local library per the Sonos FAQ, or Apple Music as a source, depending on where the music source is. 

Sorry, misread iTunes ;-)