Hello all,
I have over 500 hrs on my S-500 and thought I might comment a little about it.I think it's a step up in Sound vs nc400 and ref600m,these are the 3 class d amps that I own and I have access to more through a local audio club where we lend and or borrow equipment or occasionally listen to each other's systems.
I have been using a bel canto pre3 with all the diff. amps just to make a even playing field,the pre 3 is a pure water no coloration preamp.
The S-500 is the best class d amp I have had in my system and it has the warmest most engaging midrange with very sweet nicely extended top end that has more air and separation with the individual instruments making the entire frequency range very coherent.The bass is equally as good maybe better than my other class d amps listed.
I borrowed a Nuprime st10 to try out and found it too be a very close match to the S-500,with the nod to the S-500 for the best overall sound especially the midrange.
Offcourse this is in my system with my ears and judging the musical presentation that I prefer.
The next test will be comparison with a modwright kwa100se that I have owned for a few years but I haven't used it in about 3 years,I have loaned it out to club members though.I know it's a very good amp but can it equal or beat the S-500,only time will tell.
So many very good choices out there nowadays,
Kenny.