Just asking, you have a tube preamp, why not get a solid state amp with some balls?
I had B&W Silver Signatures for nine years. It seems to be a known thought that B&W speakers need power to fully open up.
I use a Spectron with my monitors but a lot of people don't think much of Class D amps. How about a Plinius, Pass, Threshold, etc. If you're not in a big hurry, I've seen older Plinius Class A amps come up for under $2000.00. I would think that an older Pass X150 would be in the same range. I also had a lot of success with an old Musical Fidelity A308cr power amp.
Just a thought.