To answer the question, yes.. you create a mutator using your soundpack, and have it installed on the server.
Everyone connecting to the server will download the mutator, and will hear teh same sounds.
yes but everything can just be compressed and added on the redirect so the download goes quickly (just like map downloads) Some people might remember the downloads of goatswood in the mod. textures of 40mb map of 40 mb sounds of 40 mb something like that