I don't think 20 watts will do, I have a local audiophile friend who has the parsifal encore with a 75watt tube monoblock amp(tenor) and it just isn't enough power. He loves the sound of the amp, so he is looking for speakers as we speak. I have a BAT VK-60 and enjoy it very much, I don't think I would use any other tube aside of OTL's of course, which would be my suggestion for you is to check out Tenor(may be a little too pricey but a great amp) or Atma-sphere.
Tim
Tim