2015 Sony Downmixed Audio
Unfortunately, the past few firmware updates the x850c lost a few features. Unless you are using the Video App from Sony, multi-channel audio that isn't Dolby Digital gets played in stereo (this includes DTS, PCM and AAC).
While Sony's video app will passthrough (or play the core of) DTS(HD) and transcode AAC to DD, the latter sounds like crap.
It doesn't look like Sony is going to change it back. The config for this and probably other models/years could use an update to force a transcode to AC3 (preferably at 640kbps) for anything greater than 2.0 that isn't already in that format.