If you compare the sound of a dual-layered CD/SACD as jchai suggested you'll see the difference between the two formats, which I think is significant. The problem you're hearing is probably partially the break-in, as others have noted, but also partly the Sony analog stage which, while certainly not cheaply done, may not be as good as what you're used to. I felt that way, even after a long break-in, and since I'm very enamored of my Audio Logic dac, I sent the 777ESD to Jerry Ozment, who is modifying the unit to give it the Audio Logic's tube analog output stage with a separate analog power supply (I'm sure there are others, perhaps Musical Concepts, who already have mods available for the Sony units as well). I expect it to sound significantly better (I ran the Sony as a transport on CDs through the Audio Logic to compare it to the Sony's analog stage) when I get it back. Before doing anything to it to void the warranty, though, you should let it break in and then see if you really want any further improvement.
sony scd777es and sacd
Without getting to involved with my current equipment, its all high end and well matched. My recent purchase of the scd 777es has left me a bit bewildered about the excitement of sacd. I have had the player 2 weeks and have found the sound stage thin and restricted. Although the sound is more clear without the digital haze, it has lost much of the impact my system previously had. Is it break in time or did i get caught up in the hype once again?