New speaker consideration - De Capo MM

Your 350 w.p.c. solid state muscle amp is certainly overkill when it comes to the De Capo speakers. I have owned 3 pairs of them, and currently own the Reference 3A Episodes, which use the same drivers. The De Capos have always sounded their best for me with simple tube amps, SET amps, and refined, medium to low power solid state amps like the small Pass Labs First Watt series. Great with Peter Daniels Patek gain clone amps too. The speakers should sound quite good in your small room, but if you enjoy powerful, deeper bass, you might want to consider the floorstanding Episodes. Both have fantastic clarity and extension in the highs, and a lively but slightly forward upper midrange. 

You make me worry. I just bought the De capo, it might not be a good match for my muscle amp. I might have  return the speakers and order something less efficient for my amp then

To my ears, the be tweeter is way too forward, very fatiguing and bright.  This may be the reason why a lot of owners use them with tubes in an attempt to tame the brightness.  I much preferred the previous generation with the silk dome tweeter.  IMHO, for the money you can do a lot better.  

You should not worry about having too much power. Not enough power would be more of a problem with any speaker that you decide to buy!

@yogiboy nailed it.

Having a surplus of grunt to create more headroom is a good thing, and not a weakness or liability.
As pointed out, the sonic signature of the speaker (new model with the beryllium tweeter) with the rest of your system is the synergy discussion point.

The challenge is that the identical system in different listening arenas may sound very different because of the warts and compromises of the room acoustics 

https://www.youtube.com/watch?v=BFuOxhxQ7Wo