My 2000 380DA was built w/ one external Clarion Amp and no set of entryway speaker mute switches.
On later years, probably your 2001 380DA Searay, changed to two external amplifiers and added the entryway speaker mute switches.
The line-level audio output from the stereo is wired to the amplifier(s).
On my 2000 the single external amplifier is in the compartment concealed by the screwed-on vertical cushion under the Salon circuit panel. There is plenty of room in that compartment so the pair of amps are probably located there.
The output from the amps is connected to the speakers using home speaker wiring, un-tinned copper in a clear amber insulator.
