MrMC

I've just moved to a new internet provided that also has an IPTV solution that runs on its on Android TV box. I can only get some of the surround sound formats to play properly. The others end up as 3.0 only (left,center,right).
I've got the android box connected to my TV (which does do passthrough) by HDMI and then to a Sonos playbase by Toslink. I know that the Sonos is a giant pain the arse as it only does DD and not DTS but it's what I'm stuck with.
Here's the full setup details.
MRMC 3.6.2
Telus PIK TV android box running androidTV 7.1.1 API level 25
Arcadyan Technology HMB2213PW
full specs https://www.telus.com/en/bc/tv/pik/tech-specs
Vizio D60
It can pass Dolby D, PCM, or Bitstream.

Results:
Number of channels 5.1 & Passthrough enabled for all
Dolby 5.1 works
Dolby Plus 5.1 works
Dolby TrueHD no audio
DTS no audio
DTSHD no audio

Number of channels 5.1 & passthrough only for DD & DD+
Dolby 5.1 works
Dolby Plus 5.1 works
Dolby TrueHD 3.0 only
DTS 3.0 only
DTSHD 3.0 only

Number of channels 5.1 & passthrough off
Dolby 3.0 only
Dolby Plus 3.0 only
Dolby TrueHD 3.0 only
DTS 3.0 only
DTSHD 3.0 only

I've repeated these with IEC Packed on & off with no impact on the result.
I've also repeated all of this with my TV set to Dobly D, Auto, PCM, & Bitstream - all with the same result.

I know that the source of all of my problems is the stupid Sonos soundbar and that I need to get my audio down to Dolby 5.1 before it is sent to the playbase. But I thought that would be what I would get with passthough off & channels set to 5.1.

Any suggestions?

After posting I found this question that says to set channels to 2.0 and transcode on.
https://mrmc.tv/forum/viewtopic.php?t=570

That works except for Dolby TrueHD with gives me back ground noise.

The combination of setting channels to 2.0 while wanting 5.1 sound kinda confused me.

I guess I'm OK unless anyone has an idea about the back ground noise for the TrueHD.

Thanks.