There are 2 different headlights. Most A6 C5's have single halogen or single xenon 2,5 inch lens projectors. This projector can be replaced with special projectors and brackets: Pre facelift halogen: Audi A6C5 - pré facelift (halogen headlights) Pre facelift single xenon: Audi A6C5 - pré facelift (single xenon headlights) The facelift model also has a Bi-xenon headlight with a larger 3 inch projector lens. The facelift model uses Hella E55 projectors that can be replaced with this kit:

Audi A6 C5 Xenon ballast Audi A6 C5 Xenon projector

Source: mithrilG60 on Hid Planet