The Airbus has 2 speakers, located at the end of the main instrument panel. They allow the pass through of audio such as ATC from the ACP, and also aural alerts or EGPWS (Enhanced Ground Proximity Warning System).
The speaker volume can be independently controlled by a knob on the PFD / ND panel.
The speakers are wired to also allow any aural and system alerts to override the speaker volume knob.
The next step will be to examine the circuit diagrams closely and attempt to output a computer sound card to the device.
(Thank you James and David)