The single biggest power draw on the motherboard is your CPU.
Look at the wattage of the CPU. NewEgg lists the wattage of the different CPUs in their product listings, which is a very helpful resource.
I would also check the wattage of the Zonar sound cards as part of your power calculations.
Lastly, if you intend to use an PCI cards in your system, make 100% certain the are secured in some way. You don't want a PCI card wiggling loose as your rolling down the highway.