BSPlayer has an in-build equalizer.
(rightclick > Audio > Equalizer)
Did you already use its (pre)amp possibilities?
Further, if sound is AC3, also AC3 filter has a possibility to increase volume (through "Gains" and/or its equalizer). And further, in a a direct answer to your question: yes, there are WinAmp2 DSP plugins. I recommend 'Enhancer 0.17'.
Have a look at
this post