Have you calculate per GPU power draw, I'm not sure about 1kw, I think you need more than that for those GPUs, I think there are some calculators on the web that will show or tell you how much you need, I use 6 RX 480 before, although they could run in 850 gold PSU, yours are newer GPUs, also please, check on mining section there are old post there that tells steps or shared information about it, happy mining.