Dob.... My front channels (which is all I mentioned above) has three Channel Island D200 amps (Hypex module) driving MG1.6 main speakers. For the six subwoofer drivers I have three CarverPro ZR1600 stereo amps (six channels of 600 watts/channel) each connected to one driver. I vary the crossover frequency according to the type of music: anywhere from 40 to 200 Hz.
Kijanki... With the planar main speakers, (three of them) and the three line array configured subwoofer systems, my SPL does not fall off with distance as you suggest.
There are also two rear channels, CI D200 amps (again) and Madisound Odin speakers each with a pair of 7 inch drivers (good enough for rear channel use).
As you state, loudness and dynamic range are different, but maximum attainable loudness is what typically limits dynamic range. Every system can play softly.
The best illustration of what my set of large subwoofer drivers can do is to play pipe organ music. Not all organ music has loud bass, but when it does you should FEEL it in your stomach, and my system does achieve this. Also, when the SPL is moderate, the large drivers are loafing compared with small drivers that would be generating large excursion, with attendant distortion.
Obviously I could not enjoy such a system if my nearest neighbor were not about 600 feet away with woods in between the houses.