Curious as to why you have such a strong preference for this Tara? I just feel that for this kind of occasion black slacks will never have the same festivity as a dress, no matter how the rest of the outfit is put together. What about separates? I know I usually look better in a skirt and top than I do in a dress and it usually works just as well. If there is a reason you prefer black slacks I'm interested in hearing what it is. It may very well be legit. But generally speaking there are lots of other, better options.
Also more info about the wedding would help everyone give better guidance.