You want to be able to connect 8 pin power to the cpu power header ?
Using an adapter doesn't send more power, just a signal that an 8 pin is connected
1st try using just the 4 pin ATX connector on the left side of the header ( while looking at the clip )
If the board doesn't boot you will need to use an adapter, I prefer 4 pin to 8 pin myself
but if you have a 2x molex to EPS , it should work, just don't try to overclock the smoke out of the chip