Ed,
I designed both the First Horn and the Concerti 108, as well as the upcoming Diablo, Concerti 208 and a few others. I've been designing speakers for the past 30 years or so, especially horns for PA purposes.
Atelier Speakers is Gemme Audio's laboratory. Product lines are aimed at two different markets. Gemme products are money-no-object in construction, engineering and finish, while Atelier Speakers products are oriented toward maximum sonic quality for a given price range. As such, I'd dare to say that Atelier products are probably more "design" intensive, meaning that everything is done to keep cost low while providing excellent construction and sound.
Soundwise, the Concerti was specifically designed around the Sigma driver and it will faithfully reproduce the sonic quality (and defaults) of every single component in the system. The First Horn is more exhuberent in character with big plumpy bass, and will be happy with almost all components and music types.
Anyway, do not take my word on that because I'm obviously partial. Upcoming reviews on 6Moons and SoundStage - and customers.