Manual trigger? No, to use the transcoder you need to set the audio to DD output, meaning everything gets transcoded to DD, even DTS. You would have to enter the audio menu settings to switch if you have a DTS video.
The original Ultra 4640 was capable, and you are correct that the latest Ultra models (4800/4802/4850) can as well. The 4801 (only sold at Walmart) was the exception in that it did not have the DD encoder.
The 4640 looks to have an optical TOSLINK output. So with it I can transcode DD+ to DD and output that over TOSLINK? This is actually ideal, as I'm sending my audio stream to my AVR over TOSLINK now.
The 48XX's appear to have only HDMI. I assume then that the Roku will generally output either DD or DD+ over HDMI as EDID tells it the end device is capable of?
I ask this because my HDMI splitter/audio extractor reports back by EDID that it is capable of everything (DD, DD+/TrueHD, etc). But my AVR upstream of it is only capable of DD & DTS. If I get a 48XX, I may have to set it's audio output to manual to turn off DD+. If I do that, will it still transcode DD+ channel streams to DD, or will it simple tell the streaming service not to bother with surround and revert to stereo?
Yes, the 4640 was the last model with an optical audio out. The only way to get an optical connection is to use an HDMI audio extractor.
The 4640 was released in Oct 2016, so now a nine year old model. Honestly, I wouldn't recommend buying one if you could find one, partially because it would be used and partially because Roku has made so many improvements with the later models. If Toslink is something you absolutely must have, then you either need to use an audio extractor box or look for something other than a Roku.
I'm happy to use HDMI and an extractor. I just want to make sure I can manually trigger the DD+ -> DD transcoding. Do you know if this is doable?
For your setup choose one of the following 3 options, assuming you set the extractor's EDID to DD/AC3:
Settings/Audio/Digital output format =
