I feel the ML - 336 would be the superior choice for your set up. I agree with the above - the Krell usually has a tendency to sound bright and edgy and I don't feel would be a good match with B&W. Some will say you don't need that much power (both the Krell FPB 600 and the ML 336). I would tend to disagree - the more power the better. Loudness is not where its at with power, but the current capacity and the loudspeaker control it can provide. I don't blame you for wanting a powerful amp. But again I think the ML 336 would give you great control, no coloration, and a smoothness and naturalness that the Krell would be less likely to provide. But this is just my opinion and yours and your ears will ultimately matter and count the most!! Happy listening.
Phil
Phil