Ive used the P-Zeros AO's (265/35/20's) on my S7 since new, and never had any issues. Im on my 2nd set now, and about to go to my 3rd set.
I do use Goodyear Ultra Grip winter tyres on 19" Alloys between Late November and mid March.
Recently went online hunting for the PZ's and found them to be quite expensive (like everything else these days) anything between £224 - 285 each depending on who you look at.
I did find an eBay seller, selling new PZs for under £200 each (buying 4) with delivery to local fitting centre and installation for £60 Thats quite a healthy saving over the rest of the suppliers.
- On the tyres, Audi recommendation is to try and have matched pairs per axle. You can mix brands (front and rear) but not generally recommended
- Regarding the diff - Ive been running Quattros for about the last 12 (ish) years, and never had an issue with tires being unequal rolling diameters on the same axle - i.e. 2-3mm difference, but I do try and replace in pairs if I have too, or move them around to try and stay equal where possible
- Ive not heard the one about AO only or invalidate your insurance, so Im calling BS on that one!
- Independent Audi/VW Specialists can also update your digital service record if they have the equipment to do this - Mine does (in Southampton) Usually shows up on the myAudi app with a few days.