Did you mix and match hashboards from some different miners? I think the "Voltages are different" message means the voltage settings that are programmed into the eeprom on each hashboard at the factory are not the same. The same supply is used for all 3 boards, so they can't be set differently.

Your best option is to just use 3rd party firmware like thierry4wd or vnish. They let you set the voltage and frequency, so it will just ignore the settings programmed into the hashboard.

I think to get it working with factory firmware you'd need to have the eeproms on the hashboards reprogrammed so they match.