Your profile says you are on Kyushu Island, Japan. Is the typhoon in your area? I was born in the resort town of Beppu and was raised by the snow monkeys. Just kidding about the snow monkeys!
Hope you are well.
I have no experience with the Luxman NT-07 (that you asked about in another post) but it seems very expensive compared to many other streamers with more features. In my experience the DAC (or the DAC section of a streamer) contribute a LOT more to the sound quality than the network section of the streamer.
I have a few DIY Raspberry Pi network streamers that I built and connected over USB to various outboard USB DACs. High-end brands like Bryston and Boulder use the Raspberry Pi boards in some of their expensive products which confirms for me that even the cheap Raspberry Pi can be an outstanding network streamer. Again, the DAC makes a much bigger difference for sound quality.
Customized Linux is widely used in many streamers and "Android is a mobile operating system based on a modified version of the Linux kernel and other open-source software, designed primarily for touchscreen mobile devices such as smartphones and tablets."
But... some network streamer manufacturers customize Android to better suit their DAP/Streamer product. For example, Eversolo modifies Android to completely bypass Android's audio limitations.
I believe other DAP maker do similar modifications including FiiO. I own the Eversolo DMP-A8 which sounds outstanding and is very feature rich. It replaced my separate streamer, DAC, and preamp in my system.
Here's the Stereophile Review of the Eversolo DMP-A8 Streamer / DAP / DAC / Pre-Amp
