KLH Model 5 question

Twenty five watts is a good recommendation! My KLH 6's work well with my Dynaco ST70 tube amp (35 wpc).

Being an acoustic suspension type like the Kloss designed Advent, I would say they would need a good amount of power to come alive. Here is some info on them and it says a minimum of 25 watts. 

https://stereonomono.blogspot.com/2016/06/klh-model-five.html

Those vintage AR and KLH acoustic suspension speakers were built back in the day when 25 watt (PP 6L6G's) tube amps were common. These sealed-box speakers sacrificed sensitivity for lower bass extension. Which they do quite well! 

I have AR 2ax's, AR 4's and KLH 6's. Plus the outstanding KLH Nine electrostats. They are all capable of excellent well-balanced sound!

I have the new KLH model 5's and am using a Luxman L-509au with them. It is 110 watts per channel and it is more than enough. My room is only 10' 8" X 16' 6".

I have had these speakers for a while and thought they were pretty good. But once I positioned them correctly and did some room treatment they have really come alive. These are much better speakers than I originally thought. Setting them up correctly is critical for your room is critical.