I wonder if this is the CDs? My Led Zeppelin CDs are all horribly mastered, and much of the classical I have bought isn't that good either.
Do you currently have no pre-amp? If so, you could be seeing a mismatch between CD player and amp that would be helped by a preamp.
Do you currently have no pre-amp? If so, you could be seeing a mismatch between CD player and amp that would be helped by a preamp.