How to change default music library for HomePod

When my HomePod plays, it (understandably) automatically chooses Apple Music Library, and then seems to prioritise music I have purchased from there

I don't use my AML much, therefore I would like to:

a) choose Spotify as the default music service, and/or

b) change the settings in AML/HomePod so that it plays the CDs I have downloaded there, rather than the music I have purchased

Am I able to change either of these settings?

Thank you