While I don't think I would like this particular Luxman amplifier, there is a place for tube amplifiers. I have a pair of 2-way speakers - SEAS Excel 5 inch magnesium cone midwoofer and the SEAS Millennium tweeter in a small sealed cabinet with a conventional crossover- that sound really great on a ~25 WPC tube amp I've got (Audioromy M828A, a P-P amp that uses 832 tubes) - I've tried these speakers on many other amps and there is something about the way they sound on this tube amp that "just works" - I believe that what I like about the sound is down mostly to the Ohms-law interaction of the speakers' impedance-vs-frequency characteristics with the amplifiers' highish output source impedance. This results in changes to the frequency response of the output of the amp - coloration - which to me sounds great. In addition, because tube amps generally clip in such a benign way, it's possible to get greater average SPL from the speakers than the modest 25 watt output of the amp would normally warrant, so I can get the SPL I want- which is pretty modest but sometimes louder than a 25 WPC amp would provide.. As far as "even-harmonic sweetening" goes, I don't know about that. I would say the coloration that I hear - the coloration that I LIKE - is due to the source-impedance related frequency response artifacts. The high quality, very transparent solid-state class AB, class A and class D amps I've tried did not please me as much as this little tube amp does. It's not magic, and I have done some blind A/B listening tests with a couple of people - including professional musicians - and the statistics of the "can you tell which amp is in the circuit" blind test were 100% for all the listeners that sat still for my experiment, so it is not placebo.
I LIKE the sound of this amp on these particular speakers more ( and most of the test listeners did as well ) - but that does not mean it is BETTER, MORE ACCURATE or whatever objective quality-related adjective might be used.
Could I obtain the same results with careful EQ and a solid-state amp? I'm not sure. I suspect that there is something dynamic about this impedance/power frequency-response artifact, rather than just a static boost / cut curve. Seems to change with signal content and signal level. That's just my opinion, I have no measurements to back that up.
This is a particular system I use for what is essentially HiFi background listening in an office room. My main system is powered by solid state amps, in that setup tube amps did not sound "good." (WHich is to say I did not like the sound with them.) Different speakers there, any "tube artifact" I heard through them during trials of various amps was not to my liking. In that system powerful transparent gain provided the experience I was after - solid state, in other words.