MY97 Legacy GT Wagon

I've been doing some reading on various forums about suspension options for my car. I auto-x'd my Jetta for several years and want to continue wiht the Legacy. The suspension is well worn and needs replacing if I'm going to be at all competitive. For shocks I think I have it narrowed down to KYB GR2's or AGX's matched with Whiteline springs. This is going to be a daily driver that is taken to the track on weekends.

I know they make GR2's specific to the Legacy but not AGX's. I keep reading about swapping out the "top hats" and making sure I have the right top hats.... can someone explain what they are and what different kinds suit my needs ? Can I re-use the top hats that came with my car or should I buy new ones, where do I buy new ones ?