They only work with a "PCM" Stereo Signal (Highest level is 24 bit / 192 kHz)
(You can read about that in the Manual)
They can't handle things like Dolby Digital, Dolby True HD DTS or Atmos.
So in the Kodi "Audio Settings" you have to disable "Passthrough" and set "Number of Channels" to "2"
Thanks for the info. That's the same sampling rate like the HiFiBerry Digi+. It means, lnix doesn't have to switch among HDMI and TOSLink, because HDMI transmission has no benefit for the speakers. He wants to hear music with TV switched off, so I think the HiFiBerry isn't a bad idea.