I am returning with my honest opinion on the amplifier after i have spent some time using it, listening to it. Last year I visited Singapore where they have one of the biggest shopping malls in the world, dedicated to high-end HiFi equipment, so my ear has "tasted" some very high end sound, from the likes of Magico, Aavik, Raidho, Constellation Audio just to name a few. When listening to the Nord One SE NC500 i was rewarded with a very 3D soundstage, in fact this amplifier has the most realistic sound stage i have ever heard, it's like the sound is hugging the speakers from behind. This is an amplifier with a grand sound, it has extraordinary dinamics and purity. The ultra low noise floor creates a very unique listening experience that class A, AB amplifiers cannot deliver and because of the non-existent background noise, the instrument separation is insane, not just instrument but also the space between notes it's like the is void between notes, not air. I am using mine with a pair of Dynaudio Contour 20, before deciding to place the order i was afraid that this amp would be an overkill in terms of power, boy....was i wrong. Because of the low gain factor you can crank up the volume up to eleven without hearing anything wrong, if your speakers can handle.
All of the above is valid only of the music material has outstanding quality, i have a lot of SACD material and very good quality recording flac files that have very low noise. This amplifier is like a jet, that needs jet fuel to perform at the peek of it's specs. If you feed it petrol or gasoline then you will miss out a lot of the qualities of this amplifier. I can confirm what others already said, this amplifier is super neutral and transparent, it's like a wire with a gain, if you change anything at it's input (pre-amp, dac) you will notice the difference. Usually when i read online reviews and hear the adjective neutral in my brain it translates like "dull" , but actually to my ears it sounds natural, with no emphasis on highs, lows or midrange. The bass is very strong as you would expect from such a device, but it's very controlled, the high frequency are very extended but not disturbing. In terms of resolution i can compare this amplifier to a 8K TV.
I noticed that when using it with a tube preamplifier the sound gets more body and grunt but you loose the separation between the notes, it's because of the harmonics the tubes generate. I consider this amplifier to be musical enough even without tubes at it's input, of course this is just a matter of taste.
If you have an open mind about class D, then this can be an endgame piece of fine equipment. Colin thank you for building such a high quality amplifier, for anyone in this hobby that has some experience you will appreciate and realize soon that Hypex is allowing trough companies like Nord to experience true high end sound.