Best Way to access 900 CD Collection on Sonos S2?

It’s always worked flawlessly. What you’re reading here on this forum is people who have local issues, for various reasons. Just set up your NAS, and define it as your Sonos library, and you should be good to go, like me. 

You are likely reading threads from an extended period in 2024-2025 when Sonos released about the worst software imaginable and there were all kinds of issues with local libraries among other things. 
 

The good news is you can expect local libraries to work for you now (probably)

On ripping, any portable, lossless formats Sonos supports will be fine.

A NAS is your best option. Which NAS is the harder question. 

For just a Sonos music library it is hard to beat a simple Raspberry Pi Zero running Open Media Vault. Inexpensive, reliable and minimal technical skills needed. You can just run Samba instead with minimal technical fiddling needed. Also a bigger Pi is an option if you want wired Ethernet.

A single drive NAS from any well rated vendor is a good second option. This is the least expensive but reliable, option. If using the old S1 software you need one that offers SMB v1 support. This can give you extra space for other uses and some vendors offer add-on options.

A dual drive, or more, NAS is far beyond the Sonos needs but might fit some of your other desires too.

I ripped most of my library in 2005-2006 and it’s still playing.

Edited: stupid keyboard!

Good grief!

Did you rip it with a magnifying glass and typing hexadecimal into your computer?

Hope you finish early and miss any Y3K issues.