Is the sound of an aux-connector DAC or CODEC?
This amp IC accepts analog audio input. You must have it. Obviously your audio output is analog. Text DAC or Codec refers to your case. If your audio is generated by computer software, it must be an output from a DAC (=digital to analog converter). Codec is more complex device, which has ADC and DAC.

The story in the datasheet warns that computer generated audio can have unhearable high frequency content which can interfere with the internal pulsed operation of the D-class amp IC. Some hearable mixing results can be generated and that's noise.

The datasheet guides to add extra RC filter to the input of the amp IC to reduce that noise. The filter attenuates the possible hf content of the audio.