Can if fit new 105 5700 cranks on my existing 5600BB? I am refreshing my drive train. I have been running a full 105 5600 set for a couple years. I have an ultegra cassette and chain ready to fit, and I am consdiering crankset/chainring options. Is the new 105 5700 hollow tech compatible with my 5600 Bottom Bracket?
Short answer? 

Yes, you can. Any Hollowtech 2 Bottom Bracket is compatible with any other Hollowtech 2 crank set. 

There is no difference in size or function between the 5600 BB and the 5700 BB.