My mother in law just purchased a new HDTV. And of course, the TV does not have a headphone jack. Is there a way to plug the her wireless headphone system into any other audio out source? The headphone system uses a standard headphone jack. Is there an adapter to plug this headphone jack into a composite L & R audio out?

yes, Radio shack has them. Monoprice.com will have them as well. Both places for less than 10$. The caveat is that the tv's volume control will most likely not control those RCA sound outputs. So, hopefully the wireless headphones have their own volume control.

Yeah, but what about amplification?
Unless the wireless base does, then you're not going to be able to drive the headphones with line level output.

Yeah, but what about amplification?
Unless the wireless base does, then you're not going to be able to drive the headphones with line level output.

Line output level is plenty for a pair of headphones. At full line level output you can do some hearing damage. So you better have a volume control (attenuator) on the headphones

nice! :o next time I'll stick to what little I do know!