Wow, those really are two completely different headphones. I haven't heard the D1100, but I have heard their predecessor, the D1001. I suspect that the D1100 will provide a warmer, bassier sound, whereas the KNS-8400 will give a much cleaner, airier, more treble-oriented sound. Soundstage, imaging, and detail retrieval are probably better on the KRKs, as they're intended for use as studio monitoring headphones.
Basically it comes down to whether or not you need a good amount of bass to make you happy. If you do, I'd stay away from the KRKs. If not, the KRKs might be a better option for you.
Are you located in the U.S.? If so, you could always order both from HeadRoom and return whichever one you decide you don't want.