I'm currently trying to figure out which streaming service to call home. I own about 2600 songs (not much compared to others) and it seems like trying to move those Spotify to use in their mac desktop app is just a tedious task. Maybe I don't know how to do it, but I was just wondering what others who want to use a streaming service with existing libraries are doing?
Even before I decided to give Music a try, I started to edit id3 tags in iTunes format. If a title was different on Gracenote and iTunes, I went with the iTunes naming. And I am glad I did, because when I started using Music it was looking at artist, title and album tag to match songs with their library. Please do the same to have your songs matched with Music.
After doing so, it's easy to enable iCloud Music Library on iTunes and matching starts right after that. No need for third party apps to sync music back and forth between iTunes and your iDevice. But don't forget to enable iCloud Music Library on your iDevice too.
I hope this makes your choice easier to decide. Feel free to ask if you need more help.