I've been using the Mezzmo Pro server for a long while with no problems. However, as my Sony Bravia TV is a pig for streaming subtitles (which my daughter needs) and no longer has apps such as My5, I decided to get an Amazon Fire Stick and installed the Mezzmo Android app.

The FS with the Mezzmo Android App solves the subtitles issues and the FS itself gives access to My5 etc but it has introduced a new issue.

My TV is connected to a Sony 5.1 receiver via the HDMI ARC connection but on the Mezzmo App I am only getting Dolby 2.0 showing on the receiver display. Netflix/Amazon Prime video all show 5.1 as does the Mezzmo server if I switch back to it on the TV (but then I'm back to the subtitles issue again). I'm at a loss to see why this is happening, can you help?

The FS is using the Conceivia Mezzmo (Android) profile.

Sony Bravia KDL 55W815B
Sony STR-DH820 receiver
Maxon Fire Stick 4k 2019 model