Best speaker in the $4-6k range.

Kthomas, I am running a KCT and a KAV 250p. I am also using a Marantz SA-14 for my front end.

I hate to say, I recently bought a pair of Krell 350M's to push the Nautilus 801's I have. VERY bad combo, the B&W's actually sound quite bad. I kept the amps in line, swaped out to the Energy Veritas 1.8s, and big difference, a nice improvement. Now, I am still not mad about the Krell amps!
I am using a Cal Audio MCA-2500 which is phenomenal in 2 channel for a 5 channel amp!! I am selling the 350M's and am going to try the McIntosh MC-1000's. If they don't do the trick, away they go, away the 801's go, and back to ole' faithful, the MCA-2500 with the Veritas 1.8s!

Stehno is right, Aerial 10Ts, Energy Veritas 2.8 (or 1.8) are the best speaker, IMO, shy of the Dunlavy SC-IV.

Dan

Harbeth Monitor 40s around $4.5k used, here at Audiogon.
Vienna Acoustics Strauss (the model slightly smaller than the Mahler). Vandersteen 3s. All brilliant, all non-fatiguing. Or toss the SS amp and switch to tubes.

Sonus Faber pairs well with Krell. I've seen used Extrema's on this site in that price range, they would sound great.

You could save a bit and try the Revel F30, or the F50 for more slam. The B&W's hot tweeters are probably NOT a good match with Krells, I concur. The Aeriel 7b, 8 and 10t are all good bets, but I prefer the smoother mids of the Revel.
Take a peek at room treatment to reduce low-treble fatigue, too. Have fun.