I spent the better part of a month trying to cut through the smoke and mirrors of SACDs.
i bought a highly regarded SACD player and a stack of SACDs and sat down and did controlled, line level matched A/B comparisons. I found out several things.
Initially, I noticed that sound quality was all over the place. With some legacy titles, the SACD sounded better. With others, the CD was better. Sometimes it was just different, not better, not worse.
The mastering on the redbook layer of SACDs is often totally different than the SACD layer, and both of those are usually totally different than the mastering on standard CD. This makes comparing the differences between formats almost impossible. Add to that the huge time delay in switching between layers, and the difficulty is even worse. I tore my hair out trying to find a fair comparison. Every version had different EQ. Some, like the Rolling Stones SACDs had songs that were remixed from scratch.
Finally, someone here in the forums suggested I look for Direct Stream Digital recordings rather than standard ones. DSD recordings are recorded, mixed and mastered all in the high bitrate digital domain. I got two copies of a hybrid Pentatone SACD which was impeccably recorded and mastered. I put one copy in a regular Yamaha CD player and the other in my fancy SACD player and hit play on both at the same time. I carefully level matched- the redbook was a little quieter- and spent an hour switching back and forth trying to detect a difference. I enlisted the help of a friend who is a professional sound engineer. We spent a whole afternoon examining the sound with a fine toothed comb. For the life of us, neither of us could detect any difference between the regular CD and the SACD. For all intents and purposes, they were identical.
Manufacturers have done a remarkable job trying to blur the lines around sound quality with SACD. Do they sound different? The answer is usually yes. But do they sound better? If they do, it's entirely because they have been remixed or remastered. It has nothing to do with the format itself.
I stuck my SACD player in the closet and stopped buying SACDs. It turned out that the regular CD release was just as likely to sound good as the SACD. I didn't need the aggrivation of another format for no reason.
The only reason to buy an SACD player is multichannel sound. But good luck finding a reasonably priced AV receiver that has multichannel analogue inputs. SACD is the most poorly implemented format that I've ever seen.