2001 Ls430 Ultra - Location Of Audio Control Unit

[aldenjl]

I have a 2001 LS430 Ultra with Navigation. The problem I have is with intermittent audio (does not come on initially, but once it does it works fine). I have been told that there is an audio control unit that senses the source of audio (lexus link, radio, cd, etc.) and switches the audio to the speakers. Is this integrated into the AMP, or is it a separate controller? If so, where is it located? Any ideas as to what might be the problem?