AC3filter and WinAmp2 DSP plugins are two seperate issues. In as far as I know they can be used independently from each other.
If BS.Player is using AC3
filter this should be shown (with moviefile loaded) under
rightclick > Options > Filters > Advanced.
For using BS.Player with WinAmp2 DSP
plugins please check under
rightclick > Options > Preferences > Audio > [WinAmp2 DSP plugins].
Maybe this helps you on your way.