any opionions on the Aural Thrills 300B?

Just wondering if this is as good as it sounds?
what are the least efficient speakers it would drive at concert level?
I own one of the Aural Thrills 300B amplifiers. I use this to run a pair of Klipsch Cornwall (100db efficient) speakers. Obviously this amplifier has no problem driving these speakers. I don't really know what the leaset efficient speakers would be that these amps would drive. This would be a question for Tom at Aural Thrills.

However, I will say that this is the best sounding amplifier that I have heard on my Klipsch Cornwall speakers. The soundstage is huge. The detail, dynamics, and bass are first rate. The Aural Thrills 300B amplifier trounces my Cary 300B SE monoblocks.