You can't do your own voice. You can only overwrite a existing wc3 unit's voice. Simple import the .wav as your voice and add the correct path for the existing unit's voice to be overwrited.
You can check how Blizzard has done it in their map Funny Bunny Egg Hunt
yeah just go to the sound editor,right click on a units voive file, and replace existing file with whatever sound file you have on your pc. but just to wwarn you, sound files to take up a lot of space whn importing onto a map, so dont import too much if you want it playable on bnet.