I suspect the most likely correct answer is go with none. I have a pair of bi-wired 104/2s that seem to have ample low end; I believe the 107/2s have even more. I cross over at 80 Hz to a Velodyne HGS-15 for very low frequencies such as pedal notes from a pipe organ and the LFE of films, but even without the sub the 104/2s are very satisfying. I do have a KUBE, but have never used it.
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