We had an amazing listening session with the Audionet Heisenberg's yesterday. These amps have such a super quiet background with an open/spacious sound. Image and 3-dimensional depth in that image is spooky good.
I feel the Heisenberg's are much more truthful to the music and just get out of the way. The Dartzeel (I had the 458's not the newer 468's) had a "halo" around the music making it all sound beautiful and in particular accentuating the mids.
The thing that impresses me so much with the Heisenberg/Stern combination is its ability to illuminate the inner detail in a recording without unnaturally highlighting (or peaking) any group of frequencies. I even hear this with speakers I am less familiar with. It's a magically beautiful quality.