Digitize those CDs and put them on a NAS or Raspberry Pi based music server on your network...

I did a much larger collection and it has worked great for many years. I used Compression less FLAC and they will sound like the CDs. Newer software will automatically name the song titles, and gather the album art. Digitizing will take a couple of minutes per CD. Do a few each day and you will be done before you know it.

You could do what I did and rip all of the CD music you care about onto a laptop and then create playlists to broadcast via bluetooth or wifi to your whole house system. On last count I had about 6000 songs on my laptop and I share them with my phone. All can be played over a Bluetooth receiver with a few clicks.

Well, you can buy drop-in replacements for nutone intercom, but I wouldn't.

I used some of the intercom & security wires, like to the front door, to power door cameras, etc.

I once saw a youtube video of a guy that replaced the intercom with tablet(s) for home control, etc.

I was thinking of replacing my intercom speakers with google home devices, powered by the old wires. It's convenient to say "play classic rock in garage", "Move music to kitchen" etc.

Not exactly what you were asking......

why can’t you just wire a cd player to the existing intercom system?

or simply replace the NuTone - used $800 on eBay - yeah it’s a lot of money for crap sound but there’s something to be said for not having to teach wife to use a new system - plus you keep the intercom functionality

or repair the old NuTone