These guys were a big help to me:
You will need a DAC for decent sound quality. Start with something less expensive like a Concero or metrum octave. Drive it with a good USB cable like an audioquest diamond or coffee. USB cable should be 1.5-9 feet long, no shorter or longer.
Start with a good playback software on the Mac, like Audirvana or Fidelio. Some are free. Rip your CDs to wav or ALAC format using free software tool XLD:
You may want to consider a different path. Do you really want to get into computer audio or do you want to:
"Build a library that I can pick and choose what to play- mostly for convenience & background music. Record music from some/all of my other sources. Download music."
You can do almost all of that by connecting a Sonos to your existing system (which is very nice) with a set of RCA cables and accessing your iTunes library.
Just a thought. I have considered computer audio, but never thought it was worth the time or trouble. I do like being able to play music I have on iTunes through my stereo, including CD's I have added to my iTunes library.
The most important first decision to make is what kind of format you wish to store your digital music. The best quality is "lossless" vs "lossy" (like MP3s). That could be WAV files, ALAC files, or FLAC. ALAC is proprietary to Apple, which would pose problems should you go with another operating system. WAVs purport to have higher quality, but you forgo the metadata that you get with FLAC or ALAC (ie the artist name, track name, album name, etc.).