May I suggest that the best way to see if there is something amiss with the DISC and the way in which the soundtrack is recorded, as opposed to delay that is induced by digital video processing along the line is to play the disc from a DVD player directly to an analog TV, with simple L/R audio connections from the DVD to TV, if possible. See if it is in sync in THAT condition, and then search forward from there for possible places where the delay might be coming from.

If the delay is really bad with one disc in your typical DVD > 990 > Digital Display signal path, but reasonably OK with other discs, the problem may well be in that disc.

Are you seeing (hearing!) that much more delay with this disc? Sounds odd, but anything's possible!