This is personal preference (as everything is), but they still need just as much care and attention when matching with speakers as Class AB amps do in my opinion. The lack of any character to the sound just doesn't suit some speakers.
Thanks for pointing out the painfully obvious, I was merely pointing out that Class D integrated amplifiers (ans mentioned in this thread) aren't all equal, before someone waded in and had a go.
Giving these little class D amps a nice easy load from a budget speaker is where they'll be happiest. Move further up the speaker chain and they're out of their depth. As you say, they just end up sounding flat. Found the same driving KEF LS50s with these types of amps. They're good as a...
I'm surprised the Luxman only outputs an extra 50% into 4ohms - most well designed amps with a stable power supply will double their output when the impedance halves.
Some people will believe what you tell them. If some guy on YoutTube says something is true, regardless of how crazy it is, people will believe it. And that spreads.
And to some ears, saving a fortune is as good as expectation bias.
Brands like LG and Samsung were starting to flood the market with cheap TVs - Pioneer and Fujitsu just couldn't make their TVs for less money with the same quality. People wanted cheap, not quality. Hence the TV market the way it is today.
Just bear in mind that using any amplifier with two pairs of loudspeakers means you're essentially getting half an amp for each pair. A 50wpc amp will give you 25wpc per pair. All depends on what speakers you'll be driving.