Here's what I've gathered:

Early Quantum and Quantum Z up to 1996 - Original frame with external cabling and old school style headtube for 1" threaded headset
Early Quantum II up to 1996, Later Quantum Race starting with 1997, and late Quantum starting with 1999 - Internal cable routing with and old school style headtube for 1" threaded headset (though Quantum Race starting with 1999 and Quantum starting with 2000 use a threadless steerer and stem).
Quantum Pro starting with 1994 - Internal cable routing and new style headtube for integrated headset, basically a modern alu frame.

For reference you can check out the Klein catalogs year by year at Trek, Fisher, Klein, Lemond bike catalogs, bicycle brochures