Okay, then; 25 watts has to refer not to a maximum suggested amplifier input, but to the power of the internal amplifier. The connection is a speaker level input using speaker wire, but with plugs rather than bare wire on the ends connected to the sub. The power of the receiver isn't relevant, since it isn't being used except to send the sound signals through the very high impedance(tens of thousands of ohms)of the internal sub amp input. Essentially no receiver power is used.

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Enjoy the music, not the equipment.