Thank you for your answer.
Regarding SPDIF, I use Any Luck with SPIDF/Coax? - #19 by nemoforum SPDIF output that is present on the board, especially pins 13 (SPDIF) and 14 (GND) see VIM2 GPIO Pinout | Khadas Documentation .
I suppose, SPDIF output somehow depends on HDMI. The amplifier is not connected to the TV.
USB audio cracking really looks like latency/delays because of CPU load or low priority of the audio process.
BT issue looks like a driver crash, as for me.
The mentioned issues are not critical and there are workarounds (like don’t turn the TV off and just turn off the display; use wired headphones and so on). I just tried to use VIM2 on 100% =)
Yes, I’m aware that s912 support is EOL. And I’m thinking about buying a new board. Just not decided would it be Amlogic or may be Rockchip (because of better Linux support).