Max Hi FI, I know that AR amp, Gosh Audio Research was a great company. So much better than anything else tube for so long....a labor of love I think, very difficult to make money doing it the way they did it. SP3A was a monster preamp too.
As the importer to the US for ATC, the one to try is the SCM 19, the most recent model. You'll need that 140W to light them up. This SCM 19 uses one of the lowest distortion drivers available, called a Super Linear, all hand built in house at ATC. Using a short coil/long gap type construction, it has very little coloration. The SCM19 is about twice the cost of the SCM11.
Brad
Lone Mountain Audio