Finally solved!
I installed macos 10.13.3.
Then in multibeast, enable "100/200/300 series.." and "200/z370 series/x299..", restart.
Then in multibeast, enable "alc 892" and "optional 3 port(5.1)", restart.
Audio working now!
I don't know why, but in macos 10.13.5, I tried many many guides...