Both models were compared in Future Music mag's blind shoot-out early last year (January, Februrary, or March 2005?). I'm not sure if you can access the article online, but maybe someone else here has it. I do remember that the BX5 (not the 5A) was judged highly on accuracy, but I can't remember how the KRK fared in camparison. It was an interesting and lengthy pro review, though, split into two issues.
J.