I feel the need to report my findings of my latest test. I mentioned how I once tested SACDs against the CD output of the same disks (I figured out how to switch between SACD and CD mode on my Denon DVD player), but I had done that comparing outputs with my old Schiit Modius DAC and now I have a new (to me anyway) Chord Qutest DAC. Since I don't actually own any SACDs, I borrowed a couple from my local library - really well recorded classical ones (though probably everything on SACD qualifies as well recorded) and did the same test, but with the new DAC. Before, I remember feeling that the SACD was subtly better than the CD output through the Modius. Now I feel that though the quality of the sound is maybe a slight bit different, that the CD output through the Quetest DAC sounds equally good as the SACD. Just for comparison, I tried the CD output straight from the Denon CD player which was very clearly not as good as either of the other aforementioned output... So, it seems that either a high quality DAC or SACD playback sounds better than the native CD playback on a relatively inexpensive player, but there really doesn't seem to be any specific advantage to SACDs (unless you're playing them through a multi-channel setup).
I was using my most resolving gear to listen, which consists of HiFiman Sundara headphones run through a Gustard headphone amp.
Anyway, I realize that probably most folks who are listening to SACDs are doing in part to exploit the multi-channel aspect, but as far as 2 channel listening goes, the sound quality doesn't seem to beat what a really good DAC can do with a regular old CD...