I have often heard affectionados say, tube amps have a "softer sound" whatever that means. It doesn't surprise me that most people can not tell the difference. The human eye can discern millions of colors but I don't think the ear has the same kind of acuity (in the majority of people). For the most part, I personally can not tell the difference between most high-end amplifiers. For me, a lot of the performance flaws are in the speakers, not the amplifiers.