Thanks for the research markn+. I did set Audio->HDMI to Auto Detect, and it displayed “Dolby Digital” and showed the 5 speakers. And Audio Mode is set to Auto as well.
For a test, I tried MIB II on Netflix. It came out in 2002. From what I could find, the spec for DD+ came out in 2005, so I’d expect MIB II to only be DD. On my STB, and the TV app, when I picked the movie, it showed “HD 5.1” on the title screen. When I played it, the TV indicated that it was receiving a Dolby Digital signal and transmitted a Dolby Digital signal via ARC to the surround sound system, and it sounded as I’d expect, dialog out the center speaker, etc.
When I selected the same movie on the Roku, it only displayed “HD” on the title screen. When I played it, the TV indicated it was receiving PCM audio, and the surround sound system was definitely getting stereo at most - the dialogue was coming out of both front speakers equally, etc.
So there are 2 possibilities - MIB II was resampled at some point to DD+ audio. My cable box Netflix app (FIOS) is downsampling the DD+ to DD. The TV Netflix app does the same thing. But the Roku doesn’t, and the TV can only accept DD audio via HDMI, so the Roku is sending PCM.
Or, MIB II is natively DD audio, the cable box and TV are handling DD audio correctly, but the Roku can’t successfully handshake with the HDMI to send the DD audio.
I’ll test with some other movies as well.
Also, I’m getting an amazon fire stick 4k later this week. If that sends over the DD audio to the surround sound, that’s all I need and I’ll keep that. If that doesn’t, I’ll try the Ultra anyway - it’s supposed to go on sale on Black Friday for $50.
Thanks again.