HOLY CRAP! I came to the motherboard forum to check out that same deal.
I have just made a workstation PC build order through Newegg and it just came to my attention that the GIGABYTE GA-MA770T-UD3P requires an 8 pin not a 4 pin 12V connector.
Then I looked at the spec of the Antec BP550 which I ordered as well and it says:
{
1 x Main connector (20+4Pin)
1 x 12V(P4)
1 x 12V(8Pin)
6 x peripheral
6 x SATA
1 x Floppy
2 x PCI-E
}
So I guess I am in the clear.
As for your problem, I suggest the following solution
http://www.playtool.com/pages/psuconnectors/connectors.html#4into8
If you are happy with the PSU and you have the extra connectors then by all means follow that advice I guess.
http://www.playtool.com/pages/psuconnectors/epsadapter.jpg
If you don't have an 8 pin 12 volt cable then you can use the adapter shown above. It converts a couple of 4 pin peripheral power cables into an 8 pin 12 volt cable. If you use one of these adapters then be sure to plug the 4 pin peripheral connectors into separate cables coming from the power supply. If you plug them both into the same power supply cable then you are drawing all the power of the 8 pin 12 volt connector through a single 18 gauge wire. You can often get away with that but there's no reason to do it.
Depending on the configuration, the CPU might demand something like 140W of power like in my case with the the Phenom II X4 965 Black Edition. A 140W just might be way too much to ask from one peripheral cable from the PSU, the current might melt the cable insulation and cause a nice big problem for you if the PSU controller doesn't intervene to cut you off before it happens that is.