Essentially, Stream Engine itself merely takes the compressed audio/video stream and decompresses it for other programs to use. OBS expects the stream to remain constant, but there are points where the video tends to get ahead (probably dropped frames?) and instead of waiting on the current frame for the audio to catch up, it just proceeds to the next frame. RECentral's preview window and, apparently, Amarec, properly handle the audio/video stream. Thanks for the heads up on Amarec, though.