I have heard the Watt Puppy 6's with a Levinson 335 / 380S / #39 CD player combination. Not impressed, to sterile and no sound stage. Just my opinion.
I had a KSA-250;very powerful, dynamic, but leaner than the newer Krell gear and too hot compared to the FPB series. I had the Watt/Puppies 5.1;s and used the FPB-300 and FPB-600. Both got the job done, but when I added the 600, the speaker really came alive and loved the extra current. As for soundstage, the Wilson's disappear and are superb. I upgrded to the MAXX and love them even more.
I have a ML 335 and Wilson 5.1's. I feel that the tonal balance of the newer ML stuff is a good match with Wilson's. Older Krell may be a little to upfront.
I'm not surprised by Chuck's comment. Wilson Watt/Pups are extremely finicky and take lots of work to optimize. You have to have the right room, hardware and set up or they just won't cut it. It took me forever to get mine where I'm quite happy with them. I doubt that one demo in a hundred is under optimal conditions so negative comments are to be expected. These things are just so revealing that they demand near perfect support. I can speak with experience that the mid hall sound of the newer ML works well.