As many said you need more powerful PSU for this config. Should not save money for Power Supply. I would offer the following calculations: 6xVega56 max 250W = 6*250 = 1500 + 100W Platform (CPU, MoBo, external fans) = 1600W + at least 15% reserve = 1840W.
It's only my opinion: better to have more power reserve
I understand what is the basis for the wattage calculations, but what can be done about the PSU connectors? The Vega requires 2x8 pin connectors, and they are going to run out real quick. Are there any adapters that can split a connector into 2?