Wide dispersion + high efficiency + detail + coherence in a speaker?

Depending on your budget and on the physical size of a speaker that would be suitable for your room you may want to consider the Daedalus Argos. Click on the "specifications" box on the left side of the page for detailed specs.

As an owner of their Ulysses model, which differs from the Argos mainly in that the Argos is designed to provide a much wider sweet spot, I suspect it could very well meet your requirements. I don't know what current pricing is, but as a very rough guess I wouldn't be surprised if it is in the vicinity of $20K.

Good luck. Regards,
-- Al  

Charney Audio horns. I have the Maestro with Omega RS7 drivers. All of his horns are high eff and produce clean articulate coherent bass. Charney utilizes the Tractrix theory in his designs. The horns are rear loaded and couple with the room to produce coherent, 3d,  and engaging music. No sub needed for any of his designs. I have had a number of people in my room (11x15x8) and usually the first response is "How did he (Charney) get such great bass out of a 6.5" driver?".
Zuio - All of your speaker requirements are delivered with Charney Audio Horns.
http://charneyaudio.com/  

The Zu line of loudspeakers have nearly all of what you are looking for.  I don't believe they have the wide dispersion.

@zuio --

Perhaps some older Tannoy Gold 15" dual concentric drivers would do the trick. Simon Mears Audio makes Tannoy Autograph replications with these drive units, refurbished and all, and they provide you a uniform dispersion pattern (much more important than "wide" dispersion, I’d say), true high efficiency (~99dB), detail/insight, coherency in spades, and great dynamics and bass to boot. They’re big and heavy, and will cost you at least or about $20,000/pair, but you asked for it without specifying a retail limit, and I’m giving you an example of speakers that may fit the bill according to your needs. Not least, they’re beautifully made from ground up to original specs.

auxinput,

As I recall the larger Walsh models are somewhat more efficient than the smaller ones, like the microwalsh, and overall they are not any harder to drive than most, perhaps easier. Not high efficiency like Klipsch though for example, for sure. OHM Walsh goes for extended bass in a smaller package so cannot be high efficiency.

Also, regarding coherency, I take that to mean clean integration of all frequencies for the listener. That is what OHM means when they talk about coherency with their Walsh CLS (Coherent Line Source) technology. Imaging and sound stage are different things. OHMS/omnis do those differently for sure, especially imaging. The imaging can be very focused when set up right or not so much otherwise.

Omnis and their ilk will probably never be as pin point focused as say a pair of very high quality monitors can be in practice.

The OHM Walshes go for a live like presentation in regards to sound stage and imaging, not a pinpoint one, which might occur in certain studio recording masters, but hardly ever live in real life or in live recordings.