Damping needs to be matched to spring rate.
If aftermarket springs are similar in spring rate to stock ones they will still work
properly with stock dampers. Unfortunately most aftermarket springs are stiffer.
The only aftermarket spring that still work fine with (near new) stock GTI dampers
are Volkswagen Zubehör/Driver Gear, Volkswagen Racing and Eibach Pro (European
only, not US).
Keep in mind even these work better with uprated dampers (Bilstein B6, Koni Yellow,
Öhlins) though.