I've heard three Decware amps, including the Zen Torii, and none of them impressed me. They sounded pleasant, reasonably warm and smooth, but, they seemed "whimpy" to me--lacking in dynamics and the vivid and lively quality I expect from good tube amps. The better sound tube amps are of the low-powered variety, so they may not be able to push a lot of speakers to high volume levels, but within their working range of modest sound levels, they should sound more lively and engaging than solid state amps. I did not get that with the Decware amps. They had the kind of sound I associate with inadequate output transformers.
I am not saying that they are horrible amps; they are decent for the money, but, for my taste, they are not the "giant killers" that many claim them to be. Good tube amps are not cheap because the good parts, particularly transformers, are not cheap.