As a very rough rule, I would say don't rule out amps that are supposedly too low in power for a particular application. I would at least give the Shindo a try. They make quite decent sounding gear. I tend to like the intrinsic sound quality of lower-powered tube amps much more than the higher powered amps. I have not heard a 100 watt or more tube amp using pushpull tetrode and pentode tubes that I really liked much. My favorite amps tend to be single ended triode amps, followed by pushpull triode amps. It has been quite a while since I heard the 211 amp made by Wyetech, but, I liked the sound of that amp and I would bet it has more than enough power for your needs.
If you feel that you do need more than 20 watts, consider an output transformerless (OTL) tube amp. These amps deliver incredibly dynamic and lively sound regardless of the nominal output level. It has been a while since I heard the Nagra amps, but, I would hazard a guess that Atmasphere OTLs would be to your liking; the alternative I am familiar with (Joule) are warmer sounding than the Atmasphere and probably less like the Nagra.
If you feel that you do need more than 20 watts, consider an output transformerless (OTL) tube amp. These amps deliver incredibly dynamic and lively sound regardless of the nominal output level. It has been a while since I heard the Nagra amps, but, I would hazard a guess that Atmasphere OTLs would be to your liking; the alternative I am familiar with (Joule) are warmer sounding than the Atmasphere and probably less like the Nagra.