If you have no Intervideo AC3 installed: just forget about the page with that name under "Audio" as that page indeed only applies to Intervideo AC3 and e.g. not to AC3-filter.
If you have AC3-filter installed you can access it for general setting purposes directly through: [Start] > Program files > AC3Filter > AC3Filter Config ....
but to access AC3 filter's settings from BSPlayer (with videofile loaded!) follow: (rightclick >) Options > Filters > Advanced ....