same thing here, been all over the audio drivers and can't find meaningful info from logs.
Stereo (2 channels) playback totally fine through USB device, LibreELEC correctly names the device, everything as expected. The moment I try any surround playback, DTS, linear PCM, playback disappears.
maybe there is some licensing thing with decoding the surrounnd formats? I thought hardware manufacturers (AV receivers) had to pay dolby or whoever - but it's trivial to decode in software
maybe we should flag in github?