Thanks Hock, I like the 43 Series as well and owned some 4338's before these. The new models like the K2's have Be diaphrams on the mid and treble which are to my ears sweeter than those on the old 4 Series monitors.
Also being three ways, well two ways plus super tweeter, the horn designs are somewhat more advanced making the upper reaches less coloured but equally dynamic.
As you say, the dynamics are great like many large semi horn loaded speakers (Tannoys, Klipsch etc). Where, for me, the JBL's differ from speakers I had before such as ATC, Focal and Proac to name just a few, is that that use a huge 15" paper cone to produce the fundamentals of virtually all instruments. This gives a gravitas and a "chewiness" to percussion, bass and the lower reaches of many instruments that I hear live but rarely through hifi systems.
These are basically a huge two way so they are also really coherent. I've heard monitors that image better if that's your thing but I'm more of a "tone" man.
The best way of describing them may be that if you grew up at school in the mid nineteen seventies to early eighties, these were the loudspeakers you always dreamed of owning and that probably got you staring into the hifi shop window on the way home from school
The old Album Muzzer! I'm probably showing my age and ignorance.