The Parasound JC1+s sound killer on horns. Actually, they sound killer on just about anything. The sound is airy and effortless. Sweet might be another way to describe it. They sound like very powerful tube amps but with great bass. Although the price is up to $18K they still qualify as the best value in a high performance, high power amplifier.
I bet Atma-sphere amps would do well on horns. I have not heard them drive horns but Ralph Karsten uses horn loudspeakers. They are not SS but a very different kind of tube amp without output transformers.