I have a small 10 wpc tube integrated, Luxman SQ-N150 in my office, far enough away so the heat is not problematic. Sounds wonderful. Line of infrared sight.
Just enough power here, I got lucky, speakers are low efficiency.
You can see my little Luxman on a bookcase here
I am using a self-powered sub, via speaker wires, so the amp does not get a break, only the speakers don't try to make low bass, helps them sound great.
I wish it had PREOUT, then I could use it's low power for only upper bass/mids/highs, a much smaller power load, out to a self-powered sub for power hungry low bass.
or a 'stereo pair' of front firing subs located so that their fundamentals and overtones which give directionality to bass.
OR, speakers you can bi-amp.
Raven Blackhawk has a built-in crossover, scroll down, they say the bass is 65% of the power load.
This addition to the Avian series provides an extraordinary advantage when using a subwoofer. It frees the power amp from 65% of the load it normally has to bear. This is like tripling the power of the amplifier in terms of its ability to drive speakers. It also frees smaller speakers from reproducing low bass frequencies that they really don’t reproduce very well which lowers overall distortion. This is all achieved with a gentle 6db per octave slope making it easy to achieve a seamless transition with a good quality subwoofer.It tempted me, but would not fit on top of my bookcase like the Luxman easily does."