upload a wad, or put up a directory listing of all files in the iso (to do it easily, extract everything to your hard drive, navigate to the folder with windows command prompt and type "dir /s >> file.txt" and upload said file [it will be in the folder] to stashbox.org or another hosting site, as this will provide nearly everything needed to figure out where the music is)
Ok, I use the fsbii, and it split the wad file in 4 fsb. One sounds guitar, other sounds bass guitar, other vocals and battery, and the last one is too short with all instrument (I supose it's the demo play before you begin the song).
Even if you did combine the files, you'd only then have some many channel file which probably wouldn't play right. The best solution is to decode each and then mix together the WAVs however you like.
audacity is pretty good, though you have to be careful to set it up right. By default it uses floating point and dithering. I've heard Goldwave spoken well of but never used it.