If you're comparing the analog outputs from a CD player to a DAC that is receiving digital audio data from a digital streaming source like a computer or network streamer, then the two primary aspects that could result in a difference are the reliability of digital data transfer and the quality of digital-to-analog conversion.
For example, a CD player with a poor optical drive may end up reading errors during playback. Some deeply technical computer hardware review web sites and forums will analyze optical drives for error detection and data read reliability. Whereas if you rip data to a digital file, you can check at that time that the data read was correct, even going as far as comparing the file data to other people's file data. And then reading the file data and moving it around becomes very reliable.
Digital-to-analog conversion is fairly well covered in online discussion, audio equipment reviews, and measurements.
The counter argument against digital transmission into a DAC is that a digital audio signal like S/PDIF may be subject to incorrect interpretation or timing inaccuracies. Versus a CD player where its internal I2S data stream will go straight into an internal DAC with both parts driven off the same master clock, or clocks that are tightly coupled.
There can also be other considerations at play, such as how AirPlay transmits all audio data at 16-bit/48kHz, Wi-Fi reliability issues, etc.
For example, a CD player with a poor optical drive may end up reading errors during playback. Some deeply technical computer hardware review web sites and forums will analyze optical drives for error detection and data read reliability. Whereas if you rip data to a digital file, you can check at that time that the data read was correct, even going as far as comparing the file data to other people's file data. And then reading the file data and moving it around becomes very reliable.
Digital-to-analog conversion is fairly well covered in online discussion, audio equipment reviews, and measurements.
The counter argument against digital transmission into a DAC is that a digital audio signal like S/PDIF may be subject to incorrect interpretation or timing inaccuracies. Versus a CD player where its internal I2S data stream will go straight into an internal DAC with both parts driven off the same master clock, or clocks that are tightly coupled.
There can also be other considerations at play, such as how AirPlay transmits all audio data at 16-bit/48kHz, Wi-Fi reliability issues, etc.