Ah, yeah I know it's bad enough to use 3 PSU in a row, but server PSU where I live is too costly as well as powerful PSUs, it goes for more than $400 a 1000W PSU.
The cards you're using are not cheap either. I'd understand if it's a temporary solution for you until "proper" PSUs arrive, but I wouldn't suggest you to keep using these 750w units for long.