Charles, as John B. pointed out, the 3480 has no crossover to the sub(or the mains). Although it has a sub output, it's full-range unfiltered. There are such things available as separate external filters which might be used, but this appears to be complication without real benefit. Also note that the sub's internal crossover has no effect on the speakers. If you're referring to your present speaker system, the 2105 already does the stereo function and because of its crossover provisions does it better than the 3480 alone could do.
