This was an incredibly TIMELY and useful post for me, personally! Hubs & I just relocated into a new house that came fully-furnished. It has a dedicated media room with HUGE flat panel TV set into the wall - no way to get anything behind that TV. I was disconsolate, thinking my days of TV/movie streaming with my Phonak Marvels were OVER.
There is an actual electronics closet JAMMED with all kinds of stuff here, tho, and after sharing this post with my husband (Tech Kahuna with MIT, CalTech and Stanford degrees), he tried out various connection strategies so my streamer could be hooked up but let us BOTH hear the audio. Below is HIS total tech answer - little of which I myself understand, but BOY IS IT GREAT to be streaming shows and movies again!!! 
Pardon the long post - but for some techie folks here, perhaps it will be useful?
The home theater has a number of inputs, including Roku Ultra, AppleTV, Blu-Ray, and a big/heavy TV mounted flush to the wall. The Roku, AppleTV, Blue-Ray are easily accessible, while the other home theater components are in an AV rack.
The TV does not have a digital audio output accessible (without removing the TV from the wall). Attaching the streamer to the TV with digital audio would also have a wire dangling from the TV to the streamer (not good), because if the streamer is permanently mounted behind the TV, it would be impossible to control the streamer power and volume buttons (the streamer does not have a remote - like a Fire TV Stick, that can be hidden behind a TV).
One thought was to attach the streamer to the Roku remote headphone output with a portable USB power source. Unfortunately, listening through the Roku remote mutes the HDMI sound output (why isn’t this configurable?). This is not an option, as it means that only the person using the streamer can listen. Also, this will only work for Roku, not AppleTV, Blu-Ray, etc.
Another option was to pick one video source, and split the audio from the HDMI (like this device), and connect the audio to the streamer. Unfortunately, only one video source can be used for this (changing video sources would require plugging different HDMI sources through the splitter input/output - pain!).
The final solution was actually very simple. There is an AV receiver, with inputs from all the video sources. Found out that it has RCA pre-amp outputs, which made it trivial to connect to the streamer via a 3.5mm to RCA cable. So now, no matter which video source is used (Roku, AppleTV, Blu-Ray, …), the streamer has the correct output, and everyone else can also listen to the sound.
The process was complicated by the house’s Crestron automation system, with components buried in a closet.