Do No Harm ... well the least harm anyway

Personally I would run those full range and just dial the sub in with a low crossover. Or use a DSP based low pass for the sub or something like the JL Audio crossover just for low pass,  Those are big speakers you'll be missing a lot of what they can deliver at low  frequencies and the sub can be located by ear because it is playing above 60- 80 Hz.    

Reference 3A 's special sauce is that they don't really use a crossover themselves , they use a filter cap to protect the tweeter and those woofers are essentially run full range.  I believe all of their speakers are like that. 

I like subs, but they can do more harm than good if you operate them crossed over that high. 

Why would you want to limit bass to a full range speaker system?

I'm also in the camp that prefers to run my main speakers full range, and just use to sub to augment the bottom octave or so.   Some male vocals can go down near 60hz, and are best reproduced by your main speakers so the fundamental notes plus their harmonics all come from the same place, where they stand a much better chance of sounding like a single coherent music wave. .  Just my 2 cents.

+1, @cleeds

Unless your speakers sounds distorted, I would not limit any high or low frequencies. If that’s the case, I would look at the alternate amplification (amplifier) and preamp.

OK, thanks all. My reasoning for wanting to do this is to limit cone movement of the 2 full range drivers. Since they have no crossovers at all, they must play the delicate midrange as well as the thumpy bass. I figure if I can cut out the cone movement of the bass, the mids won't be smeared by that back and forth motion. I do use subs (Velodyne DD15's) next to each speaker. Since the main speakers are away from any walls their bass is not as strong as in a conventional room. My listening room is large as it encompasses the living room, dining room, kitchen and den all in an open floor plan. I have the subs lowpass set to 55Hz.

Yes, I also realize, the other option is to leave it alone. I'm just not sure if it's better to go down this path, or not.