I'm not sure what you'd like me to say.
I was trying to explain to rawdesigns why AV playback is different from regular video playback, and give an indication on where he can start troubleshooting. His post didn't have any more info, so it's difficult to say anything else.
We regularly test sync and playback with AV files on a variety of machines. When using the default audio settings (which is 44.1 kHz sample rate and a 1024 bit buffer on most drivers), playback is no different from video playback.
If you are experiencing differently, there is something different about your setup and we have no way of knowing what that something could be. So I cannot say anything meaningful about it.
I'm not saying I don't believe you, I'm not saying that the problem is your fault and I'm not saying that we don't want to fix it. But it is impossible for us to fix a problem that we don't see.