Barry,

According to the schematics of the 3000, the headphone jack (which does have it's own Op Amp and Power Amp circuit - 0.65W 2ch) silences the speakers by triggering a Mute circuit. Each channel has a transistor switching, detected then by a "Decrease Voltage Detection Circuit" They don't use any relay. Also the Outputs (Fixed and Variable) have their own Op Amps.

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Have a nice day