1000w is to small for that.
Now im working with 5 card. So far so good.
But ive got 7 rx480.
i would not run a 6 card rig with a 1000 watts psu , your psu is working close to 95-100% with 6 RX 480 setup without proper tune , bios mod.
with a 7 cards setup go for a eVga 1600 watts psu , with 6 cards setup go for a 1200 watts psu , just to stay on the safe side