The simplest way to wire a constant-voltage system is to parallel all the speakers on only one long run of wire. But the amount of power lost in the wire may not allow the required amount of power to get to the farthest loudspeaker. And if there should be a short on the wire run, it would take down the entire system. The better approach is to wire seperate rows of loudspeakers. These separate wire runs can be disconnected for troubleshooting and could be powered by different power amplifiers.
Insertion loss is the loss of power through the transformer.
If the loss is 3 dB, half of the amplifier's power is lost. You should not have more than 1 dB loss in any audio transformer. Hz could give a false information. All transformers should be tested at 60 Hz too.