Musical Fidelity is wonderful gear but slightly forward in terms of the sound profile. It is not a brand I would match with B&W. The other issue is that it is very difficult to find lately.
I was thinking that McIntosh almost assuredly has an integrated in this price range but it might be too large.
Are you willing to consider a hybrid class D? Tube input stage with class D output stage. I have an amp that is exactly 16" deep and it is 100w into 8 ohms, 150 into 4 ohms. The Canor AI 2.10, I also have a demo of the AVM Evolution A5.2 integrated which I think is 185w into 8 ohms. It is 16" deep including nobs and binding posts. I have used both to drive Vivid Kaya 45s and they have a min impedance of 2.8 ohms so much tougher than the B&Ws. The Canor is $4K. The AVM is my demo.