They embody the idea that once you've removed everything that isn't the music, what remains is the music.
This is radical. Today's high-end audio has become all about mixing circuit topologies and parts to make a sonic blend that the designer thinks “sounds about right”. You'd almost forget that getting closer to the sound as crafted by the artist really means keeping the replay system from changing it.
Turning this simple insight into hardware is probably the toughest way to do audio. However, the result are something never before heard of in high end audio: amplifiers and converters whose output signal cannot be distinguished, by ear, from the input signal.
So what does that sound like? In a few words: natural, nimble, rich and musically enthralling.