I'm also 6'1", wearing a 34" inseam pants...and have been looking at cyclocross bikes. :-D
I tested some bikes yesterday and 58cm seemed to fit me best.
This was on a Trek
XO1. Trek has all their geometry online, so perhaps their 58 might be equivalent to a 56 in another model. Hope it works out for you.
Any bike-owning friends of similar size nearby that you could use? The difference between the road and cyclocross frames seems to be pretty minimal for sizing (IMHO).