Thanks for your inquiry. Since the Acoustimass 5 systems aren't designed to connect directly to a receiver's LFE/Sub output, it won't be possible for the Acoustimass 5 Acoustimass bass module to perform as a 2nd subwoofer for your 7.2 home-theater setup. You could connect the Acoustimass 5 system to the surround-back channels as you had mentioned. This will certainly work, but the Acoustimass module isn't going to perform as a 2nd subwoofer would, in a true 7.2 setup.
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