I've being asked by a friend of how to setup an array of speakers for a retail store. Well, I don't have a clue!

So, I'm calling the AC collective wisdom to help me here.
Let's say I want to play music to 3 pairs of (same) speakers (aligned along two walls/ceilings) at the same time. Obviously, stereo effect (imaging & soundstage) is unimportant. What do I need to get this done? Thanks.