The B&W speakers are voiced for SS amplification and are never going to sound their best with tube amplification; possibly with the exception of a pair of Atma-Sphere OTL monoblocks.We’ve got several customers that are very happy with this combination.
Our amps have a lot in common with SETs- quite literally, they are two SETs wired together differentially, with the output bridged. Triode, class A, with a character like SETs of distortion falling to unmeasurable as power is decreased. Unlike SETs they have about 1/10th the distortion, much higher power and wider bandwidth. The cost of replacement for a full set of power tubes for a pair of M-60s is similar to one good 300b.