I have tried all that i can find to force 5.1 on any other app. I only have a decoder that can do regular Dolby Digital and nothing newer. I'm using an Extron Audio Extractor to bring the audio into my system, but it only shows PCM 2 channel from any app other than plex. If I'm playing a 5.1 movie from the plex app, it runs just fine, but any other app it comes out 2 channel.
I had read somewhere that the Roku is going to try to output DD+ even when I'm trying to force it from the settings, but will default to 2 channel if my system can't handle DD+, which is what seems to be happening.
Does anyone have a fix? Or a suggestion to what I might be doing wrong?
The Roku settings are a bit misleading/confusing - they only indicate the detected/selected capabilities of the system its connecting to, not a desired level of decoding/transcoding.
The only currently available player model that supports DD+ decoding (and thus transcoding into DD) is the 4640 (the 2016 Ultra), though the soon-to-be-released 4800 (2020 Ultra) probably will as well.
You'll need to connect the Roku to another device capable of decoding DD+ (such as more recent model TVs, or an AVR, etc) so that it can/may transcode it to DD for further output.