JR, as Luis(MR)suggested, set the receiver to subwoofer, rather than both. You have an excellent sub and should allow it to have the primary responsibility for the lowest bass. The 80Hz crossover should work well and since the receiver is doing the crossover, the internal crossover in the sub would just be in the way. Since the STF-2 has a switch to completely bypass its crossover, you should set it to take the crossover out.

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Enjoy the music, not the equipment.