The CDP-S7 is internally uses a mechanism that is somewhere between a CDP-X222ES and CDPX333ES, leaning to the cheaper 222. The electronics is almost exactly the same as the X222ES. I've modded one of these and they can sound decent, to say the least. In particular, the output OPamps (originally NE5532) get an upgrade to Burr-Brown FET input parts, resistors in the differential-to-single ended conversion after the DAC get changed to metal film 1%, the integrating cap for the DAC also gets replaced by a quality mica cap, and I added decouplers to the various power supplies, as well as slightly upgraded the electrolytic filter caps. This model also comes without an optical output, but one can be added because it's provided for on the PCB.
Bostik damping panels were stuck on the insides of the case as well.
The end result was virtually indistinguishable from my modded X333, soundwise.
Even stock, it's a great little machine, though.
I think I may still have photos of the stock board and the same after the mods, I've done these for the person who ordered the upgrade.