Ok. The problem is multi-channel AAC audio. Roku only supports 2 channel AAC, and converts it to PCM. Only the Roku Ultra (model 4640) contains a decoder that can convert the multi-channel AAC to Dolby Digital. This is from their official support page:
Roku devices do not support AAC pass-through. Instead, Stereo AAC is transcoded to PCM stereo.
Roku TVs and some Roku players decode 5.1 AAC to PCM stereo for headphone, internal speaker, and HDMI/ S/PDIF (optical) output. However, Roku devices that support Dolby Audio decode connected via HDMI or S/PDIF (optical) to an A/V receiver that also supports Dolby Audio, will convert the audio to Dolby Digital 5.1.
That "some Roku players" is really only the Ultra 4640. The Ultra 4660 will not do it.
The Roku profiles contain a matches line for multi-channel AAC, so it should be captured and the audio transcoded to Dolby Digital. Exactly which Roku player are you using? Is it connected directly to a TV, or is there an AVR processing the audio? If so, does the Roku connect to the AVR via HDMI, or is the audio fed back to the AVR via optical or ARC? I may need to see a
detailed log showing the attempt to play the movie to ensure which profile line is being used.