well, there's already a way to do that,
but the thing is that the vismux plugin can't be found in the winamp plugin section, i've searched the forums also for it.
the avsociety did that for one one of there packs, do this
first duplicate the avs.dll file in the winamp plugin directory, rename it to ava.dll or whatever you want
you need to download this
pack
remember that this is the ony way to get the vismux, the pack installas alotta shit, so track it down and delete it, but do not delete vis_mux.dll, cos that's the important file,
and then open up winamp, use the vix_mus as the vis plug-in, remeber to config it to use vis_avs.dll & your copy of vis_avs.dll
then when you start the vis plugs, it will add the new avs window over the old one so you need to drag it to where you want it and then it's just chooseing which presets you want and thin it's done.
and oh yeah, you might wanna use pixeldoubling on both windows because using two windows is a seroius fps killer.
i hope you understand this, because i seriously suck at explaining