For best results you can do two things, depending on how you get sound out of your machine.
If you use SPDIF your best bet is to activate Adjust Display Refresh to match video, activate Sync playback to display and use Video Clock (Drop/Dupe Audio).
If you use analog cables or HDMI cables (while not setting your amp as capable of Dolby or DTS decoding, otherwise you fall back to the previous case and need the drop/dupe audio thing) use the same options with Video Clock (Resample audio).
Drop/dupe drops or duplicates single or multiple DD or DTS audio frames to keep the sound in perfect sync with video. If your video clock it's reasonably close to its optimum, the result is inaudible. Otherwise you might get some pops sometime.
Resample audio slightly resamples audio constantly in order to keep everything synched. Again, if you are reasonably close to video clock the difference is inaudible and you never get audio artifacts.
If you want a better idea of why we need this, check this:
http://reclock.free.fr/
For proper explanation, download Reclock and have a look at the readme file, where detailed info is provided.
The above settings combinations I've described lead to something very similar to what Reclock does (note that the link I've provided points to outdated versions of the code, but the explanation is good).