I think a good choice would be Electrocompanient either AW-180's or AW-400's if you really need mega power. They operate in class A mode up to 7 watts and don't rely on huge heat sinks. Finding them used may be a bit of a challenge though.
http://www.enjoythemusic.com/superioraudio/equipment/1210/electrocompaniet_aw180.htm
http://www.enjoythemusic.com/superioraudio/equipment/1210/electrocompaniet_aw180.htm