Dave if I follow, you're not actually talking about clipping, but instead that the receiver goes into protective mode and shuts off when the surrounds are operating. Since the surrounds put relatively little strain on the receiver, this shouldn't happen. As you mentioned, it may be a connection problem; disconnect and carefully reconnect everything to make sure that some strand of wire isn't loose, especially on the surrounds, of course.

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Enjoy the music, not the equipment.