If all you want is WAV files, I strongly recommend you use the command-line tool of VGMstream, rather than using Winamp's plugin. True, it's not a huge difference, but why bother with the overhead of Winamp, when you don't need to? It's quite easy to use too. For the simplest method, I suggest using a *.BAT file (which is a TEXT file, renamed from *.txt to *.bat). Inside the BAT file, put this:
----------------------- FOR %%a IN (*.fsb) DO test -l 2 -f 10 -o "%%a.wav" "%%a" -----------------------
Though, change "(*.fsb)" to whatever extension you want to convert.
For more in-depth instruction on how to use the command-line, and VGMstream, I suggest you read this and this - specifically, look at my posts.
Anyway, good luck with converting your files, and hopefully you'll find those links useful. Mouser X over and out.