Seems you need some sort of piped in music for your store and would only be used for background music, right? In that case, that 6-ch 40T Yamaha may indeed be an overkill. Also, the model may not be robust enough for the purpose as it is really meant for home Hi-Fi and HT entertainment and not 8 hours of continuous background music daily where no one's gonna notice or appreciate any channel separation.
There are professional PA systems in Raon that cost a fraction and have rugged designs meant for this. Then there are Electown, Sakura and Konzert integrated amps I saw at SM that cost no more than 6T and even have microphone inputs that you could use for paging in your store. I think they come in stereo and 5 channel models. And still there are great surplus integrateds at the pier for about the same price. These are mostly stereo integrated and prologic receivers. So for you to use multiple speakers scattered over the store ceiling area, you would need to do a number of series parallel connections so that the end result would be 8 ohms or 4 ohms per channel (depending on the amp's impedance requirement.)
12 Dai-ichi 10" 60 watt full range speakers shouldn't cost more than 4T. Then a 6T integrated. You probably might spend as much on the wires.
