Could it be that, since music is basically sound, and we (being animals) use sound to communicate, that music is an extreme stimulus of communicative sounds, sounds that we associate with warnings, danger, happiness, sadness, etc.? When you listen a piece of music you can tell wether it sounds happy of depressing, it can make you feel comfortable of uncomfortable, maybe it has something to do with the need to communicate with others, to be aware of what's going on in your environment, and when you listen music you make your brain think that there's danger around you, or others around you seem to be happy (because the music sounds happy). Maybe we love music so much because we need others around us and the tones that you hear stimulate our basic emotions, just like the sound of someone's voice would (or an other animal's sound).