Most 8 pin pci-e have a set of 2 pins the break away from the rest(6+2).
If it has that, then its all good, other then that, yea you would need adapter(they do make a 8 pin to 6 pin and 8 pin to 2 x 6 pin, but they are not always that easy to fine.).
You can also get the 4 pin molex to 6-pin.