I think the real issue is that decoding/altering the DD+ stream requires a paid license for the device where passing through unchanged does not. So you will only see the capability in new/more expensive hardware where the cost can be absorbed. If your TV handles DD+, it is supposed to convert to DD for optical output as part of the license requirement but I'm not sure they all do.
I think there's a fundamental issue here. These TV sticks / boxes should actually support older audio output formats like DD. This is because such devices would most likely be used with older TVs that don't support DD+. In newer TV (say models after 2017), most of streaming Apps / cast / Android are inbuilt; hence, it's less likely one would us a TV stick with a newer TV.
The Netflix in PS3 or older BD players can give the DD 5.1 although those devices are not having DD+ audio output. I'm still not sure Netflix Apps on such devices are somehow DD compatible or devices are converting DD+ to DD at the audio output over optical / HDMI (I've tested both working directly to sound system or via TV). If the latter is possible, I believe TV Stick / box makers should be able to do this with a firmware patch.
I know my kind of response will probably look to some as one of those "he's just trying to shill for Roku!" or some such. That's not the case. I'm just not clear on why the TV stick or streaming box is responsible for providing a legacy surround format. You mention the TV, itself, and an audio system. Why aren't those devices responsible for giving you a DD 5.1 (vs DD+) output? Why wouldn't a firmware update work on those devices? The sticks/boxes would need both a standard Dolby 5.1 license and a Dolby 5.1 - capable chipset - the hardware - to do this (and so would the TV and AVR).
There was one Roku box that could do this a few years ago - one of the earlier Roku Ultras that had optical out. That box could transcode/convert DD+ to Dolby Digital and feed it out over its optical port. The 2020 Roku Ultra is capable of outputting this, too, as it has an audio decoder in the box. In other words, it doesn't merely pass-through the audio in whatever format it's in to the end device. It will - if set to do so - decode the surround stream. That gives the user more options on how they want the audio output. But other than those devices, I don't know any other Roku sticks/boxes that can do this.
I'm just not clear on why the TV stick or streaming box is responsible for providing a legacy surround format.
Basically because most/all of the competing devices do it. And because the reason you are adding a streaming device is that you don't have an up to date smart TV that would have native apps.
Speaking as someone who understands all of the technical arguments being made here, I assume that most buyers of the top-rated Roku stick that have older gear won't understand the underlying limitations, and will just end up having a poor experience. They won't know, or care about, the business decisions being made that led to that outcome, they will just think the product doesn't work as advertised.
I bought mine to use in a system with an older AV Receiver, and encountered the problem. After reading this thread, I ended up returning it (to be replaced with an Apple TV). Is it that unreasonable to expect Roku to document the limitation themselves so buyers can make an informed purchase decision (rather than rely on forums like this to explain it)?
There was one Roku box that could do this a few years ago - one of the earlier Roku Ultras that had optical out. That box could transcode/convert DD+ to Dolby Digital and feed it out over its optical port. The 2020 Roku Ultra is capable of outputting this, too, as it has an audio decoder in the box.
Yes, the one had optical out definitely supported DD and I couldn't think of a reason why the optical out was removed from the 2020 Ultra. So, if it can convert DD+ to DD, that actually make-sense. Is there any reference for this?
Yes, this is true. I got a 4k firestick and solved the problem. As for researching as someone else has mentioned, that is not possible with Roku. They don't give enough information.
Also, as has already been pointed out, there are several more, probably hundreds of AV equipment that only have DD. Roku effectively will not work for them with DD+ formats. An $29 firestick solves the problem.