LM3886 parallel BTL China-mart boards?

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You are in dangerous territory...
This is a little bit complicated. First, the design may be OK. It is a well known design and has been used with servo and pot´s to even out the 3886 chips. Second, the 3886 chips are 99.9% fake.
Then be aware that the sound quality largely depends on the power supply and input stage.
If you replace the 3886 (which is quite inexpensive if you buy 15 or more from a "real" distributor) and maybe the servo OP-amps, add a 600 Watt, +-35 Volt supply (good SMPS!), You should be able to get a first class, powerful and reliable amp with 200W/8 Ohm and 400W/4 Ohm.
Have a look at the input circuit, as I suppose it must be driven balanced (or have a balancing stage).
If one chip is fake, why should the others be real?
Anyhow, usually these boards are even a bargain if you replace all parts and use only the PCB.
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I have an amplifier with two LM 3886 and two NE 5532. Classic from ebay. We can say it´s fake. It sounds into small standspeakers. Can I increase the soundquality by original IC pieces? I feel bad "resolution" agaist TDA 7293. This is from ebay too.
The problem with those boards are not only in the LM or NE but all of the components on such boards are sub par. This is comparably easy fixable (not cheap but easy) desolder all of the components from that board and carefully place it in a garbage bin. Then replace it with standard industrial components from reliable source. Low noise metal film resistors 1%, polypropylene caps and electrolytes of your choice. Obviously 5532 and 3886 need to be replaced with genuine chips. The problem with shoddy passives on such boards is one of the reasons I stopped buying them completely.
I had made a small batch (21 with prototypes) of not expensive 2 way active speakers, some time ago for sale. So tried several designs fro ebay and aliexpress, AFAIR about 5 or 6 different ones. None of them where satisfying enough to let them into the finished product as is. Finally end up making my own pcb's.

Buying just a board is much smarter choice. The only part with some value on ebay or aliexpress originated boards is 0.1 and 0.22 5W fake futaba-like power resistors. They are definitely fake as having wrong pitch but very decent quality parts if you got lucky what you got, have copper leads
You believe, that budget amplifiers sounds much better then faked board amp? A lot of amp are made in China.
That is not what I'm saying :). I'm saying that provided device will significantly benefit if parts used to build it are replaced by quality industrial parts from known manufacturers.
Or buy something that works from the start. Just an idea... ;)
Usually for my taste it have severely higher price tag :). And sound amplification stuff you buy from ae or ebay sellers work most of the time there is a issue with the quality of that work :)
But, Yes, it is completely valid idea but also this is a DIY forum :D
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