Hi Rob, There are some really helpful sites on the internet that can steer you through the minefield of offsets, wheel widths, tyre sizes and profiles www.willtheyfit.com and www.wheel-size.com to name just two, but there are others. They are relatively straightforward and you are asked to specify your current set up and then you can input your favoured sizes and the site will quickly tell you how your favoured sizes will fit and importantly sit on the vehicle. You can input as many size options as we want and as many times as you want, I was over a 12 months trying to find alloys and tyres to fit my S7 and eventually with the help of aforementioned sites I eventually found a set of wheels I liked and that would fit. No spacers, just extra length wheel bolts (from H&S) to accommodate the different offset. The other thing to bear in mind, but on an A6 (not an S6) I think you should be ok, is the physical size of the front brake callipers. For me this was an additional problem. Anyway like you, I wanted alloys that filled my arches, that didn't stick out and didn't look ridiculous. I hope I achieved it, but its very subjective!!! Hope this is helpful & best of luck