PCM 2.0 instead of DD5.1

Hello everybody

I actually use Plex on my apple TV 3 by the plexconnect link.
my problem is that I can’t have another sound that PCM 2.0 on my AV receiver Pioneer VSX 924 … instead of DD 5.1 …
can someone help me on this subject … is it due to Plexconnect or the ATV3 ??

in advance THX

Sango

PMS Preferences->Server->Transcoder->“Enable Dolby Digital on Apple TV” selected?

it works. THX