Best way is to buy a cheap Network Accessible Storage device (NAS).  The cheapest will work.

I made one form a Raspberry Pi and an using old Hard Drive I had lying about.  All in it cost £50.  All in solutions on Amazon retail around the £100 mark.  Most of these also have USB slots to transfer media too.  Once set up you can add it to Sonos and then it is an independent solution, your PC can be turned off and the NAS can be hidden away out of sight.

The effort/expense makes sense only if that music is so rare that Spotify does not carry it.

Agree.  However if you have an unstable Internet connection, or have to pay for data volumes, a NAS can make sense.  A NAS will also be a good place to store a local back up of all your precious files, such as Photos.

If you have an Android mobile device (phone or tablet) the easiest option would be to store this small amount of music on your device and play it from there. 

Playing from an Apple device would also be a solution if you have at least one Airplay compatible Sonos speaker.  

Especially since it is just 15 CDs.

Indeed. And in MP3 format, so under 2GB of data.

Hmm, okay, I’ll settle with airplay then… (just have to update my sonos speaker first :(

Weird there’s no way to play files from an online dropbox folder or something. 

I cannot upload to Spotify and play through Spotify connect? I gues the latter only plays spotify files. 

thanks guys

Another solution would be uploading your files to ibroadcast.  It is free music storage, and you can access your music from anywhere you have an internet connection.  iBroadcast is also a music service that you can activate in the Sonos App.  Works for me pretty well.

YouTube Music and iBroadcast both offer free uploading and playback of your own files through Sonos, albeit at a lower bit rate than streaming services normally offer. You can pay a monthly fee for higher quality. Apple Music also offers uploading and playback, but only with a paid account.

This is what I was looking for! Looking forward to trying this!!