log on to audi world .com ..go into technical on top of page nr forums ..in to exterier it shows pictures of how to fit s6 grills to a6surounds which may help you,, good luck

 

There are a few tech articles, one for fitting S6 grilles on a C5 4.2 (which already ahs the facelift), the other how to retrofit the RS6 grilles to fit a narrow-body 2002-2004 with the facelift. They do not help with fitting these grilles on the pre-facelift A6 (1998-2001)