The Klipsch are a naturally good idea - get the biggest model you can afford. Also, most of the horn-loaded, larger JBLs, old Atlec-Lansing speakers, and the like, plus Cerwin Vega speakers, are other high SPL, high efficiency brands.
Another idea that should work would be the DCM TFE200. At $1K/pr, they are efficient, and I heard them in a large room fed by a 25 watt tube amp. They were plenty loud and dynamic, so with your big room and big amp, maybe it would be a good fit. I think they have a 30-day home-trial so if they don't work, you cen return them. Here is a link: