The reason you don't see the problem when going through the TV's speakers is probably because the manufacturer adds an audio delay equal to the video delay they know their processing adds. Most of the higher end TV's do that now but any lip-sync error in the arriving programs and DVD's will still be there since they can't correct for that. Most people don't notice lip-sync error below about 40 ms so you can "mask" the problem getting it below most viewer's "threshold of recognition" but according to the study at Stanford University, even lip-sync error that isn't consciously noticed still causes a negative impact on viewer perception making the characters seem "more agitated, less successful, less persuasive, etc. Plus, if you really force yourself to look at the lips you will still see the lip-sync error you might otherwise avoid noticing. That's the only real way to fix it: To look directly at the lips and adjust an audio delay until its perfect but to do that you would need a remote controlled digital audio delay like the Felston, Alchemy2 or Primare. I have the Felston Dd740.
If all you want to do is make it not noticeable when using your surround sound receiver - getting the sync error below your threshold of recognition so you can ignore it - the fixed delay that a/v receivers add will probably work fine since the fixed delay inside the TV is working for you.
The easy way to adjust that would be to let both your surround speakers and your TV speakers play at the same time and adjust your receiver's audio delay until there is no echo. Then you can turn off your TV speakers.
Most a/v receivers overlay the screen with menus when adjusting the audio delay so you may not be able to adjust the delay while watching but if you can you can focus on the lips and make further adjustment to get it perfect but it changes a little between every program and DVD so if you get used to perfect sync you probably won't like the way an av receiver makes the adjustments. It's almost impossible with some and many don't have enough delay anyway. I saw one with only 80 ms total delay and my DD740 offers 680 ms (although I seldom if ever use over 200 ms)
