The LS50's are cracking speakers, I initially drove mine with a Rotel RA-11, better IMO than the rest of budget amps I tried, then I used a Primare I22 and this offerred more control & depth. Tried my Cyrus mono X200's on them, brilliant.
Now this leads to, -- I've sold the LS50's, to a friend, and she has partnered them with a Pioneer A50 amp, which is very nice, still controlled and not bright, a nice listen. So I echo what esra said, the Kefs do need a decent degree of amplification, better, brings benefits, but at a cost ! As cno has shown, there is good evidence that the Nad will be OK, best just demo them, you'll know in a few hours of listening.