From personal experience, I can say that I've especially liked my Harbeths when driven by Bel Canto amps, and by a Naim Nait 5i (though the Bel Canto is more refined and musical, at least to my ears.) Even a Rega Brio worked fine as a backup. I can't see why one would want to drive such accurate speakers with a low-powered tube amp -- that seems to me to be asking for trouble.
Alan Shaw, the designer of the Compact 7, looks very skeptically at the question of "best amps" for Harbeths. You can find his comments on the Harbeth user forum. For example, he has posted as follows: "The question of 'will this amp work with these speakers?' seems to have a life of its own. I just cannot fathom out why there is so much anxiety about grabbing any competent amp and hooking it up to your Harbeths and making great music. It seems to me that the fundamental essence of a good amp, well designed and working to original specification is that it must be relatively load-independent and the essence of a good, well designed speaker is that it must be amplifier-independent. So what's the anxiety about then? Who has planted the fear in the minds of an entire generation of hifi consumers that the amp/speaker interface is super-critical to the musical experience? With Harbeth it isn't."
Alan Shaw, the designer of the Compact 7, looks very skeptically at the question of "best amps" for Harbeths. You can find his comments on the Harbeth user forum. For example, he has posted as follows: "The question of 'will this amp work with these speakers?' seems to have a life of its own. I just cannot fathom out why there is so much anxiety about grabbing any competent amp and hooking it up to your Harbeths and making great music. It seems to me that the fundamental essence of a good amp, well designed and working to original specification is that it must be relatively load-independent and the essence of a good, well designed speaker is that it must be amplifier-independent. So what's the anxiety about then? Who has planted the fear in the minds of an entire generation of hifi consumers that the amp/speaker interface is super-critical to the musical experience? With Harbeth it isn't."