I have the Moon 600i (first version, not the V2) in a second system. It's very clean and neutral, has a nice black background and enough power and dynamics for most speakers. I have mine paired with Harbeth P3ESR.
I have no experience with Luxman or Hegel, but have compared it to a number of other integrateds including Vincent SV237, Peachtree Nova 500, Peachtree X1 Grand, and Heed Audio Elixir. The Peachtrees don't have as much detail or dynamics and the Vincent and Heed had some "grain" that the 600i doesn't.
I also have the Simaudio 430HA headphone amp which has a similar sound signature. The Simaudio gear that I've owned doesn't really have much of a "signature", it's very neutral.
If for some reason I had to sell off most of my gear and could only have a smallish inexpensive system, the 600i is what I would keep and build around.