As usual a great review! I enjoy reading your contributions to the audio world, which I initially encountered on Archimago's Musings. 🙂 Let me summarize my impressions on the latest "DSP loudspeakers":
I never was too interested in the Devialet Phantoms, to be honest, as it looks like unfinished business. As you said, the potential is there and that makes it even harder to understand why there's no complete room correction (like Dirac Live) with storable presets implemented. However, I appreciate the unconventional but acoustically effective shape of the loudspeakers. Furthermore, Devialet's marketing is absolutely not my cup of tea, I have to admit...
Similarly to the Phantoms, I see a big compromise regarding distortion at higher SPL with the Kii THREE (especially at low frequencies output), which is why also those have never really caught my interest. At such a high price tag I expect better overall performance, going beyond a sophisticated implementation of /internal/ correction by DSP.
With the Dutch & Dutch 8c we are a big step closer to what I personally would like to see in a set of reference loudspeakers.
All of those DSP-featured loudspeakers seem to use drivers from other manufacturers, unless I missed something? Of course that's not a big deal; I remember having read that the Kii THREE's tweeter (apparently same as found in the Grimm Audio LS1) is the Seas H1499-06 27TBCD/GB-DXT ; for example. [Can anybody confirm with regards to the LS1v2? There's an optional LS1be with Beryllium tweeter, though.]
However, I am sure there are more advanced drivers available as the mentioned Seas (just an example) and I would expect those latest transducers to be found on such an expensive system. For instance, JBL Professional have their proprietary D2 compression tweeter which was introduced with the M2, along with the formerly know 2216Nd woofer - to reach even lower distortion (also at higher SPL). Dynaudio just released their finest tweeter, the 'Esotar Pro' which has a new inner dome - called "hexis" - that will control the unwanted inner resonances, while also smoothing out the frequency response [found on the Core series]. We can continue with Genelec's new MDC coaxial midrange and tweeter + new woofer drivers [see 'The Ones', e.g. 8361A and W371A], Focal's Pro audio drivers [as found on the Trio11 Be] etc..
It seems the domain of distortion/resonance vs. SPL (resonances: as well regarding the cabinet) has been neglected on most reviews, which I personally find is a big miss. Furthermore, with the Dutch & Dutch 8c I cannot understand why they apply a 1/24 octave smoothing to the frequency response and 1/6 octave smoothing to the horizontal directivity plot. No smoothing at all would allow to really judge the speaker's performance; else a max. of 1/3 octave smoothing, as it comes close to what we can still distinguish by listening. Plus, why don't they provide a vertical directivity plot? [Please advise me if it is hidden somewhere, I didn't check. ^^]
Despite the difference in price, for a set of full-range speakers the JBL Professional M2 remain my reference choice and with regards to price/performance, the JBL Professional 708P are remarkable performers.
Generally, I would like all manufacturers to be more transparent and more accurate with the data they release!