This is all incredibly interesting, and if I wasn't so hell-bent on dealing with the issue of the Tesseract, I'd want to learn more.
Oh, hell, who am I trying to kid?
How do you keep the Ori at bay, if they're pure energy?
I wish you had a sample of naquadah or naquadria on hand for me to analyze, but if I were to make an educated guess, I'd say these Stargates of yours create a Time-Space Induction Channel, or Time Corridor, in which a wormhole is created through the Time Vortex. In order to complete a corridor, time conduits need to be in place that serve as the ends of the corridor. If a conduit is destroyed, you couldn't reach it via the time corridor. It's a little primitive, compared to Time Lord technology, but still effective, and I'm surprised to hear that it was found on Earth. It makes me very curious about these Ancient fellows. Are you sure there's no trace of them, aside from these Stargates?