Having sound emit from BOTH the TV and the headphones at the same time is dependent on how the headphones are connected to the audio source.  The availability of this feature is determined by the device the headphones are connecting to. Some TV's and set-top-boxes do not offer this feature.  Below are two common connection methods from devices that support this feature are:

• If using a set-top-box (cable box, DVR, etc):  Look for audio output jacks on the set-top-box, and connect the headphones to the set top box to allow for independent operation of TV speakers and headphones. 

Note: Unless the set-top-box has an independent volume control separate from the TV, you will not be able to control the volume level of the headphones.

• Check the TV manual/set up guide for an option that allows the TV to operate the speakers, and audio output jacks independently (ie: fixed output) to allow for independent operation of TV speakers and headphones and connect into the audio output of the TV.

NOTE: If you have a dedicated headphone jack and use that connection, it will automatically disable sound from the TV speakers.