Question: If what you say is true about the MTM/servo sub combo then why build the NX-Otica or NX-Tremes with separate subs? Those extra bass drivers must bring something more to the table? They must bring a bit more upper bass dynamic punch I would think.
Aside from subtle differences between the presentation and maybe tonal character of the music from 200Hz to 60Hz-ish (or lower on the NX-tremes) between the M165 and the servo sub drivers discussed above, the handoff frequency point between the servo subs and the main speakers is a key differentiator in going one way or the other for another I'd think more straightforward reason.
Because the floor standers play lower in frequency, it is arguably easier to integrate the servo subs because the necessary crossover frequency is lower - the perceptional transition between drivers may be more easily made less noticeable and one (given the space) could better place the subs for optimal bass response like more traditional subwoofers rather than woofers as part of a 3-way full-range floorstanding speaker. Because the MTM alone can't play as low, the servo subs all but have to be located as close to the MTM as possible because the servo subs are playing high up enough that if they were separated it would be significantly more noticeable.
Sure, if one could plop the NX floor standers on top of the servo subs, there is no reason one couldn't still cross over to the subs down low if one was after the presentation below 200Hz of the M165 rather than the servo subs. In this case, one would be optimizing placement of the subs simply to accommodate space in the room (the point of this thread) rather than optimizing the placement of the subs for sound (not necessarily mutually exclusive, but very room dependent).
Also, I'd think that having the subs away from the mains reduces the possible effects of vibrations from the subs making their way to coloring the sound of the mains, which obviously is not possible with the MTM if the MTM is attached to or uses the servo sub cabinet as a stand. Granted this bit is very much splitting hairs, but I suppose when trying to discuss the very bleeding edge of performance, that's where the conversation lives.
Asking Danny more directly: although you said above that the MTM is fine and you don't really
need the extra midrange drivers if stacking on top of the subs, would flipping the NX-Otica upside down on top of the servo cabinets work (need aside), or would having the extra baffle full of drivers sticking up above the MTM (and likely the lower M165 driver baffle not coupled to the floor) cause a problem with the speaker as designed because the crossover (maybe even the wings) would have to be redesigned to account for the new/different baffle arrangement? Experience being my teacher, I'd guess that answer is yes, but best to hear it straight from the designer than keep going around in circles guessing.
