The next step up the Klipsch product line used to be the Cornwall (15" woofer & bigger box) and I believe it used the same mid and tweeter horns as the Heresy.
Consider either a Thermonic 4 Pi or a Theater 4 Pi system. The old parts could be cobbled into a new system. But then you must deal with a three-way crossover and a few other problems. The costs of parts to build new 4 Pi's isn't a whole lot more than repairing the Heresy/Cornwall system. Personally, I would sell the Heresy stuff on e-bay and use the proceeds for a pair of Theater 4 Pi units. I've owned both speakers. 4 Pi now, and Heresy's a "few" years ago in my student days. Just having new drivers to work with would be a big plus.

Steve