I uploaded my CD collection to iTunes years ago and copied the music library to an external hard disk connected to the router. Sonos can access this iTunes library without any problems and play this music.

Hello is actually quite simple if you are operating the old stereo system with active speakers,
Set the output of the stereo system to Port Audio-In and the active speakers to Port Audio-Out and configure the port accordingly via the SONOS App.
If you have passive speakers (2,4,6,8 Ohm) with your old stereo system, then the SONOS port is the wrong product. In this case, I would have used the SONOS AMP.

Hello, if you want total flexibility, you would need the following:

- Streaming music from Sonos to your "old" stereo: buy a digital coax cable and connect that to your coax input at the stereo (if available), otherwise with RCA cable. Important: turn up the volume in the Sonos app (try it out) so that you can hear the music on the stereo system.
- Connect the old stereo system (e.g. tuner, tape, CD player, phono) to Sonos via a port: here you need, for example, a 4 port cinch audio switch (e.g. SpeaKa Professional SP-5741548) and 4 cinch double cables (is a Y-cable). Each device must be connected directly to the amplifier of the old stereo system and at the same time to the 4-way cinch. From the 4-way cinch, connect the cable to the In input on the Sonos port. The 4-way cinch has a selector switch at the front. There you select the music source. This way you can listen to your CD in all rooms, e.g. via Sonos One.

Have fun!

Thank you for your answer.
But I bought the Sonos Port to listen to CDs and vinyl via the stereo system with the Sonos SL One.

I have connected the port problem losmit the amplifier on tuner. So SonosRadio is perfect.

However, I don't want to have to download the CD and vinyl collection to iTunes (yet).