The Tyres.co.uk site offers a few Audi S7 options with Michelin Pilot Sport 5 energy and Pirelli P Zero (PZ4) in 255/40 R20 101Y XL, for the 2019-on S7 Sportback models which feature factory 20-inch wheels. Please confirm the wheel options, as they may vary.
For the S7 tyre sizes, refer to the driver's side B-pillar (the area between the front and rear doors) for the tyre pressure sticker. This sticker has the original tyre sizes, as well as the associated pressure and load values. Since S7 wheels can vary, double-check the tyre sidewall and the owner's manual.
While using a quattro all-wheel drive Audi S7, you may not have to replace all 4 tyres. However in the case that two tyres must be replaced, those two tyres should be placed on the rear axle, and replaced in pairs, all in accordance with the UK guidelines for tyre safety.