FWD Avant - what are my options for anti roll bars?

Can't help with your question I'm afraid but I do know, over the years, I've read a number of times that one of the best handling/suspension mods for the C5 A6 is an uprated rear anti-roll bar. Possibly the larger diameter RS6 item.
 
RS6 will not fit FWD as far as I know as needs to be quattro for RS6 rear ARB as different rear end - not much help but might clear up the doubt??