brother 4890 is a power hungry card and consume too much power and about 200watt so its crossfire will need a good power supply while xigmatek 600watt gives only about 500watt output so its better for you to get xigmatek 700watt power supply in order to run the card without any problem
and one more thing why you want 4890 crossfire ? i suggest you wait for gtx460 and when it will come 5xxx cards prices will go down at that time get 5870 or 5770 in CF