Easy man, just bought the server PSU from ebay for $ 50 -70
And add there with your solderer as many connectors as required
This ^^
Could do 6 with a single server PSU. More than 6 possible if you get the 1500W psus.
Youre better off bitting the bulllet an buying a 1600 watt evga, plug and play , it easily has enough
connectors for 6 vega cards, I buy some server psus as a bridge sometimes for my 1000 watt psus to provide
juice to some of the gpus and make the 1000 watt supplies less taxed, but I promisie you its much easier and simpler to power an atx board off an atx psu.
bunch of my 8 card rigs are stupidly unstable using server psus as sometimes when a rig reboots or dies
since the gpu still is reciving full power from the server psu it never shuts down from the error
vegas are far more stable than modded rx cards so thigh might be a non issue