[cavu]

The contractor installed 5 ceiling speakers in my new coffee shop [...] which "Votage/power" input on the transformer is best to use?

Why don't you ask your contractor??

The speaker setup you describe is intended to be driven by a 25v or 70v source. These "high-voltage" systems allow audio distribution to multiple speakers using relatively thin wiring without loss.

Check HERE for an education.

My receiver is Sony 200-Watt 2.0-Channel Stereo Receiver (STRDH100). 90 watts minimum RMS power each channel.

You will have to get some 70v transformers to hook up to the output of your amplifier to use it correctly with your speakers.

Output Voltage: 500 mV/10 kohms.

That is an INPUT voltage sensitivity necessary to drive the amplifier to full power - it is NOT an output voltage.