There is no advantage to run one big PSU with that many cards.
Those PSUs should be fine to run the cards.
They would be near the limit though the cards pull around 17A-22A each depending on the OC.
You might need 1 more small one to run the board/cpu/hdd etc and power the extra Molex adapters.
With the first PSU powering the 24 pin ATX and second PSU powering the CPU and Molex, I would think 1700W of combined power to be enough? All the cards will be undervolted.