well, 4 vegas need eight 4-pin connectors.
some vegas have 3 to 4 pin adapter included, some do not (or at least i did not find it).

EVGA 1300 has 4 single 4 pin cords and 2 'double' (4+3pin).

Therefore, either use an adapter (if available) or buy an extender. i checked an extender with single cables, making them essentially a 'double". Works fine (at least on Vega56). Might be too little (one cable) for Vega64.