I spent quite a lot of time at the ESD room in Munich last year. The room was large, and I sat well back and did not find the music too loud. The system had very impressive scale and weight, and I felt it was good at presenting almost live dynamics.
On the other hand, at the Seawave Acoustics room at Hi Fi Deluxe, they were playing at ear bleed levels, and I had to leave the room after a few minutes. In fact, my ears kept ringing for some time afterwards.
I use Classic Audio field coil midrange drivers and woofers, mated to a pair of plasma tweeters. Even though horn speakers can play loud, usually much louder without distortion than conventional speakers, there is less need to play them loud. While most conventional speakers sound dead at low volume, my speakers can maintain their liveliness and detail at low volume. This is one of the biggest advantages of horns, esp. when driven by low power tube amps. Of course, they are more impressive when playing loud, because of their wide dynamic range and lack of compression.