I own Wilson CUBs and moved away from tubes (ARC, then Jadis) recently - now have a class D ICEpower amp, from Wyred4Sound (ST1000). Stunning clarity, and absolutely grain-free. Thought I'd mention this as I love the fact that it weighs nothing, does not act as a space heater, and is great value. The sound, to my ears, has all the virtues of tubes with none of the draw-backs. I have heard Krell with my speakers, and with Sophias, and found the sound too aggressive and tiring - pretty much the "opposite" of tubes. The local distributor pushes tubes, as above, or Gryphon SS - and steers away from Krell, and ML. Of course, I'm not sure how this translates to your WP7s, but Wilson does seem to have a house sound - only improving as you go up the scale.
Good luck - I'm sure they'll sound great whatever you choose.
Good luck - I'm sure they'll sound great whatever you choose.