They are both good CD players.
The Opus 21 has one advantage of being able to by pass the volume control, by using the DIN outputs. (This is what I do, btw, in order to get the purist sound out of the unit. But that is only useful if you use a preamp, which I do!)
The Cary has one advantage of being able to play HDCDs, which I wish the Opus 21 could do, as I do have a half a dozen of these type of CDs. (Although they do seem to be fading out rather quickly.)
I doubt you would be disappointed in either unit.
Now, that being said...
If you can find the money, I would get the Audio Aero Capitole II cd player. It is the best, most analog sounding cd player I have heard. (FYI, I listen to analog mostly, so I compare everything to analog, as I find it sounds better than any digital I have yet heard.) One version even has a built-in analog input, so you could even use it as a sort of preamp, should you wish to later add a tuner, an old cassette or reel to reel tape player, or even a cd recorder, SACD/DVD-A player, or even a turntable (with its own phono preamp of course).
My two cents worth.
If you are wondering why I don't have one, it is because the Opus 21 is close enough to the Capitole II, that I would rather keep upgrading my analog system, as I feel that gets me more results. (That and the fact that I only play CDs about 5-10% of the time.)
