In a situation that where there are multiple audio components (ie: cable box, DVD, player, etc) connected and the headphones are only receiving sound from one of the audio components likely indicates that one of two scenarios is occurring.
The transmitter is connected directly into an external audio component (like the cable box) and hence can only get sound from that component. To get sound from a different external component the headphones would need to be disconnect from the original external device and connect to the other external component directly.
A solution to avoid having to unplug from one component and plug into the other component all the time you could use an AV switching box to create a hub where all the external components can be connected into one place. The hub will then provide outputs to run audio to the TV and audio to the headphones as well.
NOTE: An analog version of an AV Hub can be seen here: (http://www.amazon.com/Cables-To-Go-28750-Composite/dp/B0032ANC8M/ref=sr_1_1?ie=UTF8&qid=1393521908&sr=8-1&keywords=Cables+to+go+28750).
NOTE: A HDMI version of an AV Hub can be seen here: (http://www.amazon.com/Monoprice-Matrix-Switch-Splitter-Analog/dp/B004264PT0/ref=sr_1_3?s=electronics&ie=UTF8&qid=1372360465&sr=1-3&keywords=hdmi+rca+switch).
All of the external audio components are connected directly into a device (TV, Receiver, etc) however the devices are utilizing different types of audio signal (analog, digital, HDMI, etc) and the device that the headphones are connected to can only output some of these signals in a format that the headphones can utilize. The headphones are designed to use an analog signal so this is the type of signal that the device needs to output for the headphones to use.
The solutions that could be used here would be to try an get all the external audio components connected using the same type of audio signal and utilize something like the AV Hub mentioned above. Alternatively a component like a Digital to Analog Decoder or Digital Audio Decoder which will accept different forms of audio signals (including multi-audio stream signals like HDMI) and convert the signals back to analog for the headphones to use could also be utilized.
NOTE: A couple of the versions of the Digital to Analog Decoder are as follows:
- GEFEN Digital Audio Decoder (http://www.amazon.com/Gefen-GTV-DD-2-AA- Digital-Audio-Decoder/dp/B0021QBIBQ/ref=sr_1_2?ie=UTF8&qid=1393427713&sr=8-2&keywords=GEFEN+digital+to+analog+decoder)
- OREI Digital to Analog Audio Decoder (http://www.amazon.com/Orei-DA34-Digital-5-1-Channel-Headphone/dp/B008EPW7O0/ref=sr_1_2?ie=UTF8&qid=1393427822&sr=8-2&keywords=OREI+da+34)