You cannot legally convert protected AAC files. Protected purchases from 2009 or earlier can be burnt to CD and then ripped back into iTunes. Content from Apple Music can only be used in iTunes or the Apple Music app on suitable devices while your subscription remains active.  If these are from Apple Music, the best way to play them is by streaming through your Apple Music account on the Sonos app or via Airplay. 

Thanks for the info, however, any suggestions on a process to play music from pc to Sonos, trying to avoid streaming/internet due to outages?  

The Sonos folks would likely get all soggy and hard to light if someone was to post a tutorial on cracking DRM protected content on their forum.

You might find that elsewhere on the web but I’d really recommend against doing it.

If you do rip the music I’d suggest going to a lossless format, without DRM, so you do not surrender any music quality.

Soggy and hard to light? That’s a new one on me, but I like it. You Arizonans…:)

The other option, depending on the age of the file, is to delete the local file, and download a ‘fresh’ version from Apple. It’s been quite a while, but several years ago they removed DRM from a lot of files, but they didn’t replace the local version, if you’d already purchased and downloaded it. I remember at some point I had to re-download a lot of them…but once done, the DRM is gone.