I bought an original Apollo back in early 2007. It was a great-sounding player but right out of the box it had a bad transformer hum. While it was in for repair I was lent a Saturn by my dealer... and that was that. I said "Keep the Apollo." to the dealer and bought the Saturn instead. The Saturn simply gave me more of everything without sounding off-puttingly different to the Apollo.
15 years on, I still have the Saturn. It was re-lasered around four years ago, it's still in great condition, and it still sounds as good as new. Well, actually, it now sounds better than new because rest of my kit has all been upgraded and is better able to show off what the Saturn can do. I can safely say that my Saturn isn't going anywhere.
If I wanted to improve my CD sound today - which I don't

- then I'd look at plugging the Saturn into an offboard DAC instead of replacing it.
(I have an Audio Note DAC 0.1x offboard DAC connected to my Bluesound Vault 2 and it slightly edges the Saturn in sound quality, but only when I perform comparisons. In everyday use the Saturn remains superb.)
So, for you, and
subject to an audition if possible, I'd suggest a good used Saturn R as a valuable and straightforward CDP upgrade that comes with additional benefits. The bonus is that the Saturn R's DAC can also be used separately, thus setting you up for a wider range of sources of digital music.