there is no such thing as overkill when it comes to low bass. if you calibrate the subs to the same SPL as the other speakers, 2 will help even out the frequency response in the room, that is if they are opposite each other in the room. All you have to do is hook the "line out" on one sub, to the "line in" on the other sub, or use a splitter at the receiver "sub out" jack, and have two seperate cables.

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