Using older Cary SLA-70 sig with fantastic results. Mine is switchable pentode/triode, and my experience has been that triode IS the way to go with the Klipsch speaker. Conrad Johnson would also be a good choice. However, I don't beleive that ARC would be a good match. Audio Research gear is quite "linear" sounding and tends to sound cold and hard with horns. ARC is more suited for difficult loads and more "current" speaker designs. Anyway, good luck.
