Seems to have same problems as some of u and nobody seems to have found the solution already.
I have a LG uh610v TV (arc but not atmos) and the SJ9 and a Mibox3.
My miBox3 is plugged into the SJ9 hdmi in and the tv is plugged in hdmi out arc of the SJ9.
CEC is activated.
So far I have DTS as well as DD and DD+ sound woking fine. However on atmos audio file or truehd, no sounds only video. Moreovee kodi doesn t seems to identify that sj9 is capable of atmos because it doesn t (the option for teuehd passthrough are not shown).
That lead me to the conclusion that the sound is passing from the mibox to the sj9 then to the sj9 to TV, then TV resend the sound through arc to the SJ9 which plays it. Because my tv doesn t support atmos it cannt passthrough