Hi I owned WP 6's for about 5 years. Now have WP 8's.
I guess you have to decide first if you want tubes or solid state or maybe tube pre and solid state amp. Your Wilsons are VERY revealing of anything. I am assuming you set them up perfectly according to the manual? If not, I'd pay a Wilson deal to set them up. It makes a big difference.
Do you want to by new or used? I had recent issue with one of my amps, barrowed a BAT VK300x integrated amp. It was killer. Tube pre, solid state amp.
Lots of combo's from ARC, BAT, VTL, Ayre. They all sound a little different. Certainly the NuForce you've heard is a consideration. This is hard to decide, it's best to listen some, but I know we can't always to that.
Also, do a search here on Watt Puppies. Several have asked before.