Originally, a CD player was just that... a CD player. They could play the discs and provide an analogue output to connect an amplifier. Nothing else would connect to it (except external D/A converters) and it couldn't play anything else.

Following the emergence of music streaming and other means of playing digital music, some manufactures sensibly started adding digital inputs to their CD players. This means that you can now make use of the high-quality D/A converter inside the player to get superior performance from these other digital sources.

Today some of these fine CD players also include Digital Audio Streaming capability offering the advantage of a single high-performance digital source in an elegant package, with all the flexibility you need.