After looking up on newegg I wouldn't be happy.http://www.newegg.com/Product/Product.aspx?Item=N82E16817371006
Notice that the EA430 has only one PCIe plug. The GTX560TI needs two. They must have used a Molex to PCIe adapter to get it to work. And for me, a new machine shouldn't need any adapters.
You're pretty close to the limts of what your PSU can do. I don't think a hdd will put you over the edge, but you are much to close to the limit for a new machine. I'd take it back and see what they will do about getting a better PSU in there. Depending on the CM 550W PSU they were going to use the Antec might be better. But at this point I wouldn't go adding much more to that machine.