This “device” allows you to stream your audio to the server and loop it back through a simple set of audio cables. This will include the D/A and A/D conversion necessary for the audio to go through those cables. This can be used to simply test your audio streaming, analyze the conversion, or possibly add conversion harmonics and artifacts by driving the A/D converter slightly hot.
This device is not necessary when using other equipment. All equipment will have dedicated A/D conversion and ports that are included by default.