In some cases, the HT/surround sound system may have a built-in delay to adjust the audio sync. You might check to see if your setup has that option available.
I have a new LE40A856 TV. sometimes when viewing the voice/sounds synchronisation does not seem correct. I am using a surround sound system and not the TV for the sound and the picture is from a sky digi box . Do I need to adjust any TV settings ?