Guy, as some of the previous replies have indicated, to get proper bass to the sub when you're playing in stereo mode you should set all speakers small on the 772 with an 80Hz crossover, and the low pass filter on the sub should be turned all the way up to 150Hz so that it doesn't interfere with the 80Hz crossover that the 772 is doing. Despite the suggestions in the manual, deciding whether to set speakers large or small based on their physical size is nonsense and should be ignored.

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Enjoy the music, not the equipment.