What kind of B&W speakers do you have?
You know Rotel & Classe amps would mate really well with B&W, depending on your budget. But Classe Delta series amps are huge and you said you have limited rack space? Then a used Classe Sigma Amp2 class D amp would fit perfectly in your rack, it is small in size but it's class D amp and I'm not a fan of class D amp. While the Classe Sigma Amp2 sounded great but to me it sounded kinda dry due to class D design I think, but it is smooth though considering it is class D design amp.
Naim would be another perfect candicate for your B&W and all entry level Naim amps are pretty compact in size except for its 500 series amp.