I think you are referring to the open baffle speakers of PureAudioProject. I like those speakers too. They are available with alternative choices for the midrange/high frequency driver. At 96 db/w they could be used with some low-powered single ended triode (SET) amps, with some limitation on playing at extremely high volume levels. Still, if they create an opportunity to use 300B SET amps, that would be more avenues to explore.
I am a big fan of many high efficiency speakers because they tend to sound more lively and open sounding. These include horn-based systems and systems using full range drivers in either single driver full range systems or as a wide range driver in multi-way systems. For single driver systems, I particularly like those of Charney Audio. At somewhat higher price points I like the single driver and two-way systems of Songer Audio (field coil full range driver).
Klipsch Forte IV's are not my favorite horn systems (a bit too rough and they have a peaky midrange), but they are very lively and fun sounding speakers and I recommend them at their price point. They sort of require decent tube amps to tame their harshness and most people never hear them at their best because they are not normally matched to very good tube amps.

