Horn speakers , high efficiency but not “shouty”

Yes you can crank up the volume with Charney Audio horns. As with any speaker your room will determine the effect. The Volti’s will play loud and clean but lack emotional engagement to the music/artist. More of a pro-sound if you will. The Charneys will draw you into the music and relate what the artist’s intentions are. It’s the difference between someone who can play the notes (Volti) vs someone who has command of the instrument and their personality is revealed (Charney).
I own Charney Companion horns and very happy with them.

newtoncr-You mentioned purchasing the Excalibur which driver are you considering?

I have posted it before, but will again:

Horns belong on top of poles at high school football stadiums, period.

I challenge you to A/B your horns with any model of Magnepan speakers and see if you still want the horns.  Listen especially to voices and "quiet" instruments.

If so, fine.  If not, maybe you can move on from them.

Cheers!

Just like some ears prefer the characteristics of vinyl - with all its known colourings - so might some prefer the sound a horn gives them.
Speaking for myself, my very large back-loaded horns are perfect for the large room we live most of our life in. My monitors in the studio are perfect for that task. My line arrays are where the band moves about a lot. Different colours for different listens.
The key thing is to couple the driver(s) to the room in the right way for you. 

PureAudioProject Quintet trios with Voxativ widebanders. 5 watts extremely loud, user adjustable XO and EZ caps changes. Not shouty. 

I like Maggies too, but, as is the case with all speaker types and models, they have their own set of strengths and weaknesses that may not fit the particular priorities of any given listener.  For me, the biggest issue is that they come alive at a volume level that is a little bit too high.  The other issue I have with them is that they don't pair well with the type of amplifier that I much prefer--low-powered tube amplifiers.  I've owned Maggies, and can very comfortably live with them, but, I prefer the particular horn system I've assembled.

The Charney and Rethm systems the OP is asking about have very limited distribution and are really only known to audio cognoscenti, while Maggies are ubiquitous.  I am pretty sure the OP and anyone who are interested in them have run into Maggies before and for whatever reason, are not considering them.