stickman451,
The above 3 posts and my own are all from Klipsch Forum members!
I myself started a long time ago with a pair of 1998 Oiled Oak Klipschorns and a Velodyne HGS-18II sub. Later I added a second Velodyne HGS-18II sub, and then I added a pair of Klipsch TSCM's. TSCM stands for Theatre Stage Corner Monitor and is a rare, theatre Pro Version of the Klipschorn. Presently, I am running seven TSCM's, two Klipsch KPT-684 subs and the two Velodyne HGS-18II's, so in all, I am running six 18 inch direct radiator drivers.
The post right above mine is excellent for what you need :)
I would also restate that if you have not already bought your subs, that your Klipschorns will sound even better with a horn sub woofer than a direct radiator will. The biggest obstacle you might have is space! Some guys are running smallish Table Tuba Horn Sub Woofers. If budget is not much of a problem, and IF, you have a HUGE room, You might consider something as wild as a Klipsch KPT-1802 which is a 7 foot wide Horn sub for Theatres. KPT stands for Klipsch Pro Theatre, and some guys already have one in their home with Klipsch Jubilees.
I really have to just ask, why you asked hear, and not on the Forum, as you have obviously previously joined?
Best of luck with your project, and if you want a lot more responses, or have other questions, feel free to come back and ask us :)
Roger