Do you indeed have Intervideo AC3 installed,or are you just referring to the intervideo tag in BS.Player (under Preferences > Audio > Intervideo AC3). If you don't have Intervideo AC3 settings on that tag will not work. In such case you should install AC3 filter instead. For settings of codecs/filters actually used by BS.Player for playback you can check (with a video-file loaded!) under
(rightclick >) Options > Filters > Advanced (also click on the [+]-s).
Will search for this plugin so that I can try (not to-day anymore)
Note that you can only load/config a plugin with a video file loaded!