We send out kits from duals to quads and typically they are in pairs. We've owned and heard them all as well and tell you remember this.... in moderately sized room, adding more drivers is not necessary for SPL, dual play plenty loud enough in 2stereo h-frames but, adding more drivers to reach those same SPL's will reduce the workload of each woofer. Now, the servo subs are already extremely quick but, when the workload of each driver is reduced, the settling time is reduced even further. You are also adding surface areawhich will help increase impact aeven at lower listening levels....
With regards to stereo pairs, yes, it makes a huge difference. A single h-frame will work , and it will work well but, add that 2nd tower and run them in stero and you wil be amazed at what happends
jay