Since the DSP is a CS4231A,...
Actually the DSP is an SAA7705H. The CS4231A is a codec.

The CS4231A is used to sample analogue inputs into the empeg, eg Aux In, tuner etc so that the visuals can be used. Note that the DSP is still responsible for the audio related to those inputs.
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Mk2a 60GB Blue. Serial 030102962 sig.mp3: File Format not Valid.