Is a Sonic Frontier Power 2 a "differential amp"

I believe it is a differential amp. However, you should try contacting Chris Johnson of Parts Connexion. Here is the president of Parts Connexion and he also ran Sonic Frontiers, he still does mods and repairs on SF gear.

Can't tell you about the design. But it was one of the worst sounding amps I ever owned.

Shakey

This review in Stereophile states that it is a fully balanced (differential) design.

Shakeydeal is out of line. I researched his thread history and he mentions that every amp he used sounded better, but never mentioned other electronics, etc. that would have an effect on the synergy of the sound.

What did you have in mind for the amp? I've heard it many times back when it was in production. Its very well made. Weather its the right amp for you really depends what you like and how you will use it.