If you can tolerate a decent amount of saddle to handlebar drop, the 56cm frame will probably work for you. FWIW, I am 6'0" and ride a 55cm frame but I do not mind the 10cm or so drop that I have. If this bike is a Defy series bike, the headtube lengths are pretty generous and the drop may not even be an issue.
FYI: Road bike frame sizes are typically given in centimeters, not inches.