Whereas the Pass Labs preamplifiers are designed by Wayne Colburn, the power amplifiers are the work of company founder and high-end audio veteran Nelson Pass, who even lays out his own circuit boards. The X-model amplifiers, beginning with the X1000 in 1998, were the first implementation of Nelson Pass's patented Supersymmetry topology (see "Nelson Pass on the Patents of Pass"). The XA series, which debuted in 2002, combined Supersymmetry with the single-ended class-A operation of the Aleph series. The XA.5 models offer detail improvements over the XAs.

I've loved the neutral, detailed, involving sound of Sonus Faber loudspeakers for as long as they've been available in the US. Most of my listening to them, however, has been at audio shows, and during a visit to Audio Research Corporation in 2012. (Since 2008, both ARC and Sonus Faber have been owned by the Italian firm Fine Sounds SpA, and since then ARC has used speakers made by SF, as well as by Wilson Audio and Magnepan, in the design of their electronics. Fine Sounds also owns 100% of Wadia, McIntosh, and Sumiko.)