Do you intend to put in a whole-space background music system? A paging system? Just a few speakers here and there with a gong kind of sound?

Whatever you do, if it's more than two or four speakers, use PA equipment and 70 volt speakers. And no, "70 volt" does not mean crappy sound (unless you're only going to spend five bucks on each speaker!).

One of my clients uses a Gilderfluke product -- a stereo SD playback device with built-in 20 watt per channel Class D amplifier. It can be programmed to play something with a voltage pulse. Just to demonstrate its versatility: she wanted Buddhist chant music to play in the entry when someone walked in. I put a PIR sensor in the room and set it to trigger ramp up of volume followed by ramp down thirty seconds after the last pulse from the PIR.

It's been "playing" for maybe a dozen years at this point. No moving parts. If you used this and replaced the chant with a gong recording, you'd have a push button controlled gong sound.

Yes, this is NOT a 70 volt product, but Gilderfluke probably has 70 volt amps, too. They're worth checking out just for the cool name, great logo, and bizarre panoply of products.

EDIT: Cool. While I was writing, Mac came up with a probably cheaper way to do the same thing.