unheard of brand. Save your money and get a Sony.
I thought Japanese stuff was supposed to be really good?
I don't know about this system but I have an Onkyo Amp and CD player for my hi-fi and they sound amazing. The amp won a 'What hi-fi' award for 2017. So unless something is really wrong at Onkyo, I'd assume this system would sound great.
This Dolby Atmos or Dolby Atmos? Dolby Atmos is awesome, Not every Atmos sound track is awesome but there are very many good ones, quite a few very good ones and some awesome ones. I don't know about "This" Dolby Atmos speaker. Up-firing speakers do work very well when set up correctly and you have the right type of ceiling. Onkyo's first attempt at up-firing speakers are universally described as not bad at best so at this price and with their past effort, I don't hold out too much hope for these but you never know...
it's great and there's more content (at present) for that than DTS-X, but the speakers will work for both formats (if they are in fact 5.1.2 as others have mentioned), but of course do you own research etc, depends what you watch from which sources etc