I have an old Yamaha YSP-4000 that can handle dolby digital. But many new movies are in Dolby digital plus and whenever they are it goes bad
I have Rpi 3 running latest osmc that have an hdmi to my Panasonic TX-75FX780E and from that I have a toslink down to my soundbar
The only was I can “fix” the sound and get voices (Center speaker) is to go into settings on OSMC and change from 5.1 to 2.1, but this gives very bad muffled sound compared to real 5.1
In Audio settings I have "Dolby digital plus E-AC3 capable receiver set to off
If I play from the TV directly it gives me surround with the same file so it seems to be a OSMC/Kodi issue
It’s more likely to be because your TV doesn’t covert DD+ on HDMI to DD for Toslink. Most don’t.
Have you got AC-3 transcoding enabled? If you enable that and set channels to 2.0 you might get a better result.
Actually it is more a TV issue being caused by how you set up Kodi. That setting is how many LPCM output channels you can support. Toslink only supports two channels so when you tell Kodi to send out anything more than that your TV has to downmix that to send it out the Toslink (and according to you not with great results). If you set AC-3 transcoding as grahamh suggests above then Kodi will send out a bitstream instead of LPCM and your TV should just pass that along without remixing it.
Apparently I was ruining it by doing 2.1. I found No Dolby Digital Plus (E-AC3) passthrough saying it has to be 2.0 when using toslink, so now it works