Whole house multi room audio

I have a home with many rooms and speakers previously installed when constructed. They all terminate in a single equipment room but have never hooked them up to an amplifier or anything. I always thought crestron and such were way expensive for a fairly simple solution not yet available. Now home sharing, airplay and that remote application, seems there should be a fairly simple way to provide a multiroom amplifier feeding the sources, say 8 sets of speakers and use an app to control what source in itunes and volume control for each set of speakers? Any ideas?

Thanks so much