ok! that SHOULD do
the power requirments on ur 4890 is 500W while the whole system is running.
The nex thing i need to know is the brand.
If that passes you can go ahead and buy the extenders and its best u connect what ever needs to be connected. Underpowering ur card can fry ur chip...or starve it to death.
heres wat i dug up on the card -
*500 Watt or greater power supply with two 75W 6-pin PCI Express® power connectors recommended (600 Watt and four 6-pin connectors for ATI CrossFireX™ technology in dual mode)