If 400 watts into 2 ohms would work for you, a CODA Continuum Stage+ amp would be an excellent choice. It's stable into fractions of one ohm. Has powerful, tight bass and great delicacy in the mids and highs, too. See this site for more info:
http://www.coda-continuum.com/product/index.html
http://www.coda-continuum.com/product/index.html