the 2 main qustions now please
1- will the 2nd and 3rd group of cards work fine even their atx socket on the mobo is not connected
2- will the adrenaline driver make 10 cards work well or i'll have stability issues ??
socket B and C is only for syncing the ATX PSU
it WILL work without 24pol in B and C
only be sure you plug in the molex A B and C
i have 10 Vega running fine with 18.6.1 and tried also with 19.4.x (only problem is missing power_temp - so i still use 18.6.1)
try to sell the EVGA PSU, get yourself a smaller one platinum and server psu and you are ready to go