I saw this on ebay. it is an upgrade for A6's to the S4 control arms. My questions are this: will it actually work and will it improve the handling?

 

That sounds fishy. The A6 is a lot heavier then the S4, I donno how that would turn out. specialy from Ebay.

 

I just got mine done and the uppers were definitely the same, at least that's what I was told when Mike changed mine. You might want to contact mike@vastperformance.com, he may be a bit more expensive than ebay, but you'll get the right parts for your car.