Kef R-3 owner questions

Picked up a used pair a few months ago. Thinking about moving from my integratedt to a higher powered stereo Amp with a pre. Large open untreated room, listen to all sorts of music, no way to treat room. Using Kimber speaker cables, transparent interconnects. Source Thorens MKII 160, Lexicon SACD, and Innous Zen mini. Curious to try tubes in the pre-amp. Any experiences and suggestions from owners (or others for that matter)?