De acordo com a minha versão do zip man-page, você precisa usar dois pontos para separar os sufixos:
-n suffixes
--suffixes suffixes
Do not attempt to compress files named with the given suffixes. Such files are simply stored (0% compres-
sion) in the output zip file, so that zip doesn’t waste its time trying to compress them. The suffixes
are separated by either colons or semicolons. For example:
zip -rn .Z:.zip:.tiff:.gif:.snd foo foo
Então você acabaria com:
zip -n .mp3:.wav:.3ga main_expansion thaisounds