[fritsch]

Everything. Yes, from kodi pov for sure: Go to Audio settings, set them to Fixed, choose 5.1 and e.g. 48 khz. With the "fixed" setting everything will be put out as 5.1 pcm from kodi, channels not existing  are filled with zeroes. E.g. if you play a stereo 2.0 stream with "Fixed", kodi will output FL+FR and LFE, SL, SR are getting zero samples. Obviously under the box we still rely on AudioTrack / Android firmware doing the right thing.

If your question was not really "always" bust mostly, plain disable Passthrough and kodi itself will only output PCM audio.