I understand know, I was originally thinking of testing the DC side, but you are correct, the AC side (after the inverter) will be 220V or 110 per pole. With all the variables, panel angle, clouds, time of day, the best I can hope for is equal output from all the inverters.
The main breaker has to be on for the inverters to work. I do not think testing with a known device input will work.
Thanks eveyrone.