For the dual core CPU you should be able to use the 4 pin Quads require the 8 pin.
The problem with adapters is that your pulling twice the wattage through the half the wires. But the dual core will draw less then the Quad.
Without a Video card you should be ok on the wattage.
Pull the board out and do the bench test don't skip ant steps>
How to Bench Test Your System