I'd strongly recommend the KRK KNS-8400s, the 6400s' bigger brother. I believe they fulfill all your criteria. Very detailed and well-extended on both ends of the spectrum, but darn near neutral, to my ears. No over-exaggerated bass, but impact and depth are still excellent. $150 on Amazon.
Edited by Marximus - 6/15/12 at 6:57pm