This DSP Plugin, 'Compressor & Wider 1.1 for Winamp' works fine with BSPlayer, I use it all the time. It works with any kind of audio source (MP3, AC3, OGG Vorbis, etc.) and with BSPlayer Build 498 or higher it also works with Movies with multiple audio streams.
http://www.rz.uni-frankfurt.de/~pesch/