I could be wrong here (I really hope I am,) but I don't think that any version of DSM truly supports direct Airplay. I have the streaming icon showing at all times no problem, but herein lies the problem:
If I use the DS Video app on my iPad and launch the video, set it to stream to the Apple TV, it plays fine. If I shut the iPad down, or close the DS Video app, the stream continues until the buffer runs out, then stops. I tested a few times, and it seems to take anywhere from 1 minute to several minutes for the buffer to run out, depending on how soon I shut down the app after initiating playback.
Same goes for playback from my mac: I navigate to the Diskstation in firefox or safari or chrome, and once I start streaming to the Apple TV, playback only continues while I have the browser open.
Seems massively inefficient: Playback streams from my Diskstation through my wireless access point to my laptop, back from my laptop and through the access point and out to the Apple TV. Not to mention the CPU overhead that the transcoding on the DS entails.
I don't want to fry my access point and potentially take out a city-block of power just because I decided to stream an HD video. Seems like there should be a better way.
Please correct me if I'm missing something here