AMP or Preamp

I have not heard a set of Wilsons like you have before - but I’ve heard from associates on other forums that the’re awfully nice / revealing.

It sounds like you already have some pretty decent sources, and the Power Amp that you have could be better, but it’s no slouch either.

If I were being "semi-practical" - looking for high quality, but VALUE = I would be looking at some of the BHK Signature products from PS Audio (Hybrid Tube / Solid State - taking advantage of the properties of both in a "synergistic" combination) Maybe start with the Pre and upgrade to a nice pre-owned set of monoblocks to replace the Rotel Amp later.

Another two decent brands to try for Pre-Amps (Line-Stage) would be Audio Research and SimAudio Moon -
I have heard a local high-end dealer’s demo system - with Vandersteen Model 7 speakers being driven via Audio Research Reference tube components and other goodies. (That was a system in excess of $100,000 retail) The imaging and black levels were almost "spooky" - but for that kind of moolah, they SHOULD be!
The solid middle-of-the-road Audio Research stuff or older, refurbed Reference stuff might be attainable

But with a system like yours and the amount of your budget - I would certainly:
-Audition a few units, to see what sounds best with the rest of your Sys
-Only buy from places with a good Return Policy, so that if you don’t like the way it sounds, you can return it for a (at least nearly) full refund.
-Find a forum with other Wilson Speaker owners, and see what has worked for THEM.

If you want to keep the system "sleek" = minimize the number of boxes to be interconnected, I have it from a reliable source that I trust (a different local HiFi dealer who carries a wide range of price options) that the Hegel integrateds are awfully nice.

Good to hear that you did whats absolutely right. Started with the speakers. I would be careful spending a lot of pre/amps to begin with. Buy some cheap and good class D like XTZ Egde. Then you have power enough. See how you like it. Don’t need a pre to the Vault. The next is your room. Adding a professional room correction unit would make wonders to your overall sound. And will also educate you in sound/listening. No speaker presents a correct frequency curve in a normal listening room. 

I second asking Johnny at Audioconnection. He knows just about everything out there, even if he doesn't sell it. And, he won't denigrate it, either. He'll give you an honest answer even if he won't make a dime.
One of the best...
Bob

It seems nobody has anything negative to say about PS Audio, Audio Research and Pass Labs could be a good place to start.  

All three would be good choices.  Wilsons are extremely revealing of upstream components, so I would try several if possible.