Secondly, I look at the specs - and although I am not a real spec man - the 84 db S/N ratio seems really low as does the thd measurement of .25 - 2% at max output. Would an amp with these specs seem 'quiet'? Would I hear hiss thru the speakers if I went up to them? A solid state amp with these specs would be trashed....
It is pretty well known that the ear can reliably hear distortion of 0.5% on steady-state pure tones. For music the results are not so clear. Various studies have shown that most listeners can't reliably identify distortion on music of < 1% to 2%. Keep in mind that speakers will have distortion levels 2 to 3 times higher than electronics.
Regarding the noise level, I doubt you would hear any tube rush through MLs with 89-92dB efficiency even if turned up to max gain w/o a signal. Of course I'll ask, what purpose would that serve?