Best speaker brands for transient response

Yes Volti is a very good brand for delivering excellent dynamics and speed while still sounding relaxed and natural.  This is a far cry from a brand like Zu which is very fast and dynamic but also shrill and brittle sounding (to me anyway).  Volti horn systems are the rare examples of modern horn compression driver systems that I like.  However, there are MANY vintage systems and drivers that can sound as good or better than the Volti, although many are quite expensive.

JBL horn systems can also be quite dynamic, but, they don't have enough mid-bass weight for my taste so they sound a bit thin and slightly harsh; still many, like the Everest are very much worthy of top end systems.  Fyne speakers sound fast and reasonably balanced and just a touch harsh.  There are quite a few high efficiency wide-range driver systems (i.e., not compression driver/horn systems) that are also very dynamic, such as the single driver and two-way systems of Songer Audio, the single driver backloaded horn systems of Charney Audio, and the single driver and two-way systems of Cube Audio (I particularly like the two-way Nenuphar Basis model).

At a lower price point, the MoFi Source 10 is quite dynamic with only a slight bit of harshness.  It won't deliver the weight and sense of scale that the Volti speakers deliver, but, they are surprisingly capable.

A dealer in the Washington DC area, Deja Vu Audio, builds custom speakers using modern and vintage components.  These can be tailored to one's specific taste, which is a BIG advantage of a custom build.  They employ vintage midrange horns and compression drivers because there is very little out there that can match these old drivers except VERY expensive drivers from the like of G.I.P., ALE, Cogent and Goto.  These systems truly deliver excellent dynamics while retaining a sweet, natural and relaxed sound; the weight and sense of large scale is particularly good when very large format horns are employed (some of these horns are monsters).

The interesting thing about horn systems is that they sound particularly good at lower volume levels and tend to work well in small rooms--controlled dispersion of the mid and high frequencies help to lessen the impact of room acoustics.  Big horn systems in tiny rooms are common in Japan where rooms are small and listening levels have to be kept low to not disturb neighbors.  I don't see the 12-foot distance to the speaker as a big problem.  Still, I can understand the anxiety over not having the right to return the speakers if they are not to your liking (they have a sound I think almost everyone will like, but of course, you may be the exception).

Even if you get to audition candidates, if you don’t hear them in your own room, you still have that uncertainty.  It would be hard to find dealers who have the speakers you are interested in and are will to loan them out.  I see how the Mofi speakers are less of a risk at the much lower price and a chance to hear them at the dealer.  I hope that works out.  It would be an even better audition if you get to hear the speakers with your amp; perhaps the dealer will allow this.  The amp-speaker interaction is particularly important to the sound.

I agree that ribbons and similar planar magnetics subjectively have very good transient response and can sound very good.  I too like the Divas.  These types of speakers make a good case for disregarding measurements as they have the worst waterfall plots which would suggest the opposite of clean and fast decay of notes.