09-18-08: Audiofeil
Low powered tubed amplifiers are a better match for horns than class d amplifiers.
Onkyo, Pioneer, Sansui, and Kenwood notwithstanding.
That's my formed opinion based on experience.
Nobody said anything about Pioneer, Sansui, or Kenwood. Your lumping of the Onkyo--and the incredible job they did with the A-9x55 series--in with them is desultory and dismissive.
The question wasn't an invitation to audio snobbery, but rather an inquiry whether a higher powered class D amp is categorically a bad match. I cited a professional review into very high sensitivity horn-based speakers powered successfully by the Onkyo. The high switching noise typical of a class D amp would make for a bad match with a high efficiency horn, but Onkyo of all the class D amp designers has put together a couple of features to lower the noise floor--a large, powerful analog power supply, and a patented circuit to mirror the switching noise and thus cancel it. Robert Deutsch's review verifies that it works. He also tried a $1500 Flying Mole class D and reported that it was unacceptable, and nowhere near as good sounding as the Onkyo.
That one might ultimately still prefer SETs is a separate issue.
It seems the old VTL Tiny Triodes would be a good matchup for such a speaker as well.