It is not required, but it is considered good and reliable engineering. In practice, it has been shown that systems with an output transformer are less susceptible to electrical failures, and are less sensitive to temporary short circuits that occur on long lengths of 100V PA systems. Also, a balanced signal is used to reduce as much as possible interference with other signals (fire alarm signals, etc.). The quality is satisfactory because mostly the most important thing is to transmit speech information, music playback does not require HIFI.
In any case, I would suggest to the OP to use several smaller transformers connected to one output of the amplifier if there are several incoming 100V lines and not one large transformer, and to try using toroidal transformers with a ratio of 1:1 (115-115V). 1.2kW on 4 ohms is approx.
