Is possible for me to change the game sound effects? I wanna change the ion cannon sound.

It is (I think), but I don't know where the files are, srry

Its possible, somewhere in the whole sfx xml list.  Just Look at the extractor, and you'll see a whole list of files pertaining to sfx.  just extract the ones you want.  The sounds themselves are stored in a .meg files, so you'll have to add the file to that folder and stuff.