My Hi-Fi amp is one of thier class AB models, but I have no doubts that the class D units sound just as good. Your class AB amp is very nicely made, but it appears to need fans for cooling, unless they only operate at high temps? Either way, thier operation will spoil the low noise floor desired for serious listening. I think you'd have to hear a class D model against a class AB one of similar quality, i'd like to myself. As for valves, i've never really heard them either, but isn't the deal with them that they have more distortion and noise technically, but usually sound more "musical"?