Best amp under $6k, in your opinion?

Here are a few:

Bryston 4B SST stereo or 7B SST monoblocks (used)
Nuforce Ref 9 V2 SE monoblocks
Belles 150A or 350A Reference monoblocks
VAC 160 Musicbloc monoblocks (used)
VAC Phi 110/110 Stereo (used)
Spectron Musician III MK 2
H20 M250SA monoblocks

All of them would work very well. The best is up to listener preference.

You should also ask SP Tech for their recommendation.

Tvad, whats your amp at the moment?
I wasnt overly impressed with the Spectron MIIISE. Is the MkII that much better?
The others I havent heard.
H2O looks interesting.

the spectron blows away the H20s. Plus, anything I've had tube or solid state!

Philefreak,
what source and speakers do you use. Is it MIIISE MkII?

Perrew, do you have a preference for SS or Tubes? If tubes, and if your speaker really have that smooth an impedance curve, you might want to consider an Atma-Sphere MA-1 (used), another excellent tube choice would be a used CAT JL2, which does care much what your impedance curve is, but flatter and higher is better for all amps - and a Music Reference RM200 or RM9 which would be well below your price point but competitive in terms of sound quality with much more expensive gear. The Quicksilver V4s would also be a great choice and drive your speakers with ease. On the SS side, and given that you proabably need 100 watts with your speakers I would look at either used Ayre or Pass XA amps, though the Pass may be above your price point to get enought power. My 2 cents.