5.1 passthrough on LG optical out

Anybody with a LG 65C7 who uses the optical output? I wanted to use it as HDMI extractor to feed audio to my processor since it's a neater way and without the issues of extractors. However, it seems that at least this model only outputs PCM in either of the "PCM" or "Auto" settings. The service menu has options for Dolby, DTS and TrueHD modes for the output, which points toward this being supported, but regardless the output is still only PCM. Any ideas? Source is a Mede8er where there is no options of audio encoding on the HDMI output side.