Replacement CD Player?

Oppo UDP 205? It is not only a very fine CD player, but it will also play many other formats, up to and including UHD Bluray (for your opera recordings, or to get good sound playing movies on your TV). It also has additional digital inputs, if you want to add something like an external streamer. It has a variable output, so you no longer need a pre amplifier, and both rca and xlr connections.

If I’m only interested in using it as a CD player would the 205 be worth the extra expense over the 203?

The biggest difference is in the audio part. But you have a cheap alternative. Since your Meridian 561 DSC has an optical digital input you only need a pretty basic cd player, as long as it has an optical output (or coax if you are willing to put up with a - simple - coaxial to optical converter). The part of the cd player that is responsible for the sound quality is essentially the DAC (digital to analogue converter), and you already have that in your Meridian 561 DSC. In fact, you also have optical inputs on the speakers  - I am not quite sure how these units combine. What is the purpose of the 561 DSC?

The 508-24 was one of the best in its era. I'm not sure that $1500 would capture what the Meridian had to offer. The Hegel cd-only players are at the top of the game today, but expensive. Rega, Arcam, and Cambridge Audio, as well as Marantz and Yamaha are making very fine players these days.