Water leak shorted out audio system - '99 A6Q Avant

[Pontiffp]

California's rainy season has been making up for lost time these past 2 weeks.

Although I haven't found water on the carpet, I have found quite a bit of condensation inside the windshield, and the left channel of my Bose system sputtered and went quiet. Now only the lower right front door speaker is working.

I tested the sunroof drains and the drains beneath battery & power steering unit, all of which flow freely. The plastic cowling beneath the windshield "may" have been 2mm off the glass near the center, but I'm not certain, as I pressed down on it before examining it carefully.

Main question: where is the most likely source of a leak that would short out all but 1 speaker? In one archived posting, I read that there is an amp in the right rear panel. Others state that each speaker has it's own amp. If the latter is true, then I'd think Head Unit is likely problem.

Any suggestions?

Thanks in advance.
Pableau