Green Mountain Audio Callisto fits your question perfectly. I have driven them with an AES Superamp with 15 watts and now drive them with a Cary Rocket 88R with 30 watts in triode. The Rocket is 10 times the amp in sound quality and speed, but the Callisto sings with both. First order crossover with 90-91 db effeciency and the most satifying speaker I have owned in 30 years. See the 6 moons review:
http://www.6moons.com/audioreviews/gma2/callisto.html
http://www.6moons.com/audioreviews/gma2/callisto.html