For playing Muzak in a business he could ask a professional audio contractor. They specialize in these systems and have all the proper info.
Now we have wireless and cat5 systems. But you won't find these products in a music store or at Radio Shack. It's a specialty industry that's a sub set of being an audio engineer, contractor, installer.
Example TOA, Factor, Erickson Commercial,
But that said most Cafes have a cheap getto blaster and run undersized wire into a bunch of plastic speakers (2 ohm load ??) and seems to work fine.
Blue tooth will be the only choice at the low end of things.