After muchwith various people, I have found a solution. Basically, I have found that a headphones jack cannot be added to the P42UT50 because its speakers are alleged to be hard connected to an internal circuit board, and secondly, any attempt to hook up headphones off the set itself will fail because as its internal speakers are turned off by menu selection, all external audio outputs are also turned off. That leaves the only solution must come off the HDPVR.
Off Memory Express, for $39, I bought an HDMI Splitter with audio out:
Ultra High Performance 3 Ports HDMI Switch - $39
The audio output from this HDMI Splitter emerges super quiet, expecting to be input to a home theater system with its own amplifier. Having no desire to buy a home theater system, just to be able to plug-in headphones, I found a headphone amplifier for $24.
Headphone Amplifier - $24
This little headphones amplifier has all the cables needed, has its own volume control and bass boost, works like a champ.
In use, I simply "mute" the internal TV speakers, then plug in my headphones into this tiny little amplifier, an 'voila' , headphones behave normally.
Solution quite acceptable, and at reasonable cost.