Sync problems
The sync problems you describe are related to the video processing of your HDTV. To perform the de-interlacing, scalling, etc. of video, some TVs introduce several frames of delay. This can cause the the audio signal to get there before the video causing a "lip-sync" issue. To compensate for this problem, most new receivers include an audio delay in the range of 0-200 ms. For example, all Yamaha receivers in the last couple years have included this feature.