I am one to avoid snake oil and things being over-hyped myself, but different CD players sound different. Saying that digital signals have been 'mastered' is rather naive.... just like analog signals.

Dealing with analog signals may be mastered, but any turntable maker knows you have to put a ton of money into analog to make everything sensitive enough to pick up the information on the record.

In digital you can easily have sloppy amplification, regardless of up-sampling. Converting digital to analog can be very noise if there is a cheap OPAMP anywhere in the circuit.