A very easy and informative read.
It's called a six piece system, and it's seven pieces if you count the 1kW sub amp/active xo/parametric EQ/bass curve EQ.
Duke's preferred "Two Streams" label is descriptive. One highly directional on-axis line of sight array (front firing) + a discreet, totally separate, late-arriving, full range system (rear firing) for reverberant field.
The following just occurred to me in the last week, and I'm surprised it took so long for the light to come on (or should I be not surprised?).
Another long-held architecture exists for exactly the same "Two Streams" paradigm, and one in which I have hundreds of hours of listening experience: The Live End/Dead End acoustically treated sound room (LEDE). The general design of such room is for the front third (speaker end) to be treated to be as acoustically "dead" as possible: all boundary surfaces are treated to be as anechoic as possible. Conversely, all remaining two-thirds of boundary surface is untreated, for a "live" acoustically reflective effect. The front third has thick carpet and pad, the rear two-thirds of the floor is hard and reflective.
The point of an LEDE sound room is to damp as much as possible all early reflections, followed by high level of properly delayed reverberant field w/spectral curve similar to on-axis output. "Sound" familiar? (No pun intended.)
Over about three decades, in VMPS' LEDE sound room, I heard the best and largest VMPS speaker models, from the VMPS True Ribbon (British Strathearn mid array), to the 5 foot BG ribbon, to the RM-60 Wing, and everything in between. I modified a large living room into a quasi-LEDE sound room, the difference being the entire floor was carpeted.
I prefer hearing Duke's speakers w/his "Two Streams" architecture (four models prior to Bienville Suite) in regular listening rooms more than any LEDE experience. The stage is significantly deeper and wider, and I believe pitch sensitivity is greatly enhanced. Greater pitch sensitivity shall make you enjoy musical experiences you currently find boring. This happened to me many times. Bring a complex classical music disc to this room and check for yourself. Image specificity might be a toss up, but something about the imaging seems more natural w/Duke's architecture. One other item favoring the TS architecture is much higher sense of being enveloped in the musical experience, and more pleasurable involvement.
In both cases there is simply more of the original recording venue (whether real or synthetic or parts of both), and less constant "thumbprint" of the playback sound room. When changing discs, you are bound to notice a greater difference in the acoustic effect.