The AD-500W uses the CRYSTAL CS-4340 Digital to Analogue Audio decoder chip.

This chip takes care of everything to do with the audio side of your 500W.
It is a 24-bit, 96 KHz DAC which takes in the serial digital data stream and converts it to an analogue 2-channel output.

The audio chip is located on the circuit board here, partially hidden by the transistor:

Get the CS-4340 datasheet HERE (in PDF format)