I don't get LRS and cheap Ayima AO7 amp

You will hear much much more with a real powerhouse amp. 

I've been using exclusively those tiny class D amps in my main system and in my bedroom system. In the main system, tri-amped, I use a TA2024 tripath chip based Trends TA10.1, heavily modded, with a good linear PSU, and it sounds absolutely marvelous. 

When my friend purchased his vintage Audioreference 126Dc speakers, they sounded like crap with his existing Musical Fidelity amp... we tried one of my tiny class D (SMSL SA50, 70$) and it sounded MUCH better (poor synergy with the MF amp, probably, but still, we are talking a 3000$ amp vs a 70$ Chinese "gadget").

My budget is low, before switching to those little marvels I owned and tried many vintage / not so vintage class AB amps, some class A as well, but they were either disappointing OR unreliable. 

I'm not saying those are the best amps in the world, far from it, but the right ones sound very good, give them clean power from a linear PSU and they will impress, tweak them a little (capacitors, volume pot...) they will shine. For me, when you add on practicality, foolproofness, and the fact that they use almost ZERO electricity, there's no way back.

I also use a Chinese DAC (Gustard A18) and it is also incredibly good for the price (around 600$).

Keep in mind that the high end world is often about chasing the last few percent of performance. If you spend 10 times as much, you don't get 10 times the performance.  This is true whether one is talking about stereos, photography, cars or sports equipment, etc.  And we also can't forget the pride of ownership angle (i.e., snob appeal) that comes from owning fancy and expensive gear. Plus, some stuff is just more fun to look at than other things. 

One more thought regarding the "appearance" angle.  I had a client some years back whose only products were high-end writing pens. Their cheapest pen was $3,000, and their most expensive cost $85,000.  I don't think the pens wrote any better than what you could buy at Office Depot for a fraction of that, but their main use was as jewelry for men.  Think about it, jewelry serves no practical purpose other than appearance, yet people are willing to send thousands, tens of thousands or even millions on it.  

In audio gear, there is always the sound quality issue, but it doesn't stand there by itself.  Just as with jewelry, one can run up the price of a stereo component with what it takes to attain a certain appearance.  And that is without even discussing how the price tag can also be arbitrarily inflated just because of the brand name.