Audio Physic, the original anyway, are a funny brand. Damned difficult to set up properly, but if you make the effort, they pull a dissappearing act second to none. The first designer of the brand, Joachim Gerhard was charmng, dedicated to his craft, and mad as a brush. He would talk about sitting in a room, endlessly listening to speaker cone material falling against his work surface, to decide which one had the best sound.
And those original AP's were something, fast, effortlessly musical, fantastic with voices. I had the second pair of Steps imported into the US, and they were the best speakers I ever had.
They're a little dry so they sounded best with tubes, but with a 4ohm impeadence, they really liked more power then your average tube amp could give. Even my McIntosh MC40 mono blocks struggled with them when you turned up the wick.
For a SS amp, I think you need a minimum of 100 watts for any of them, preferably something like a Pathos Logos.