Probably the biggest evolution in CD players is the use of CDROM drives and buffering the data before spooling it out to reduce jitter. Similar to the way Computer Audio works.
The biggest evolution in digital audio is elimination of the optical disk completely. Better retention of the music data on hard disk, and better SQ is possible in the playback due to lower jitter.
Jitter is the #1 problem with digital audio and there have been great advances in the last 5 years to minimize this. It can never be zero, regardless of what the marketing BS says.
The next major milestone is to properly characterize jitter and its audiblity.
Steve N.
Empirical Audio