From the First Watt site, where Nelson Pass says it best:
First Watt exists because I wanted to explore a variety of amplifier designs in what I think of as neglected areas - amplifiers that might not fit into the mainstream and are probably not appropriate to my more commercial enterprise, Pass Labs.
With oddball characteristics and output power ratings of 25 watts or less, First Watt is not for most people. If you have efficient loudspeakers, listen at reasonable levels and are obsessed about subjective performance, then you probably have come to the right place.
The reviews of these amplifiers are all stunning. Raves keep coming from so many different reviewers. Do a quick web search and get all of them. A perfect match for the Cube Audio speakers, with enough power to drive to an unreasonably loud level.