Ah my apologies, the S-Line suspension is also dropped by 15mm as well. You're running S3 Rotors which are 18''/7.5J/ET54, with 12mm & 15mm spacers, then your offset is now ET42 & ET39. My alloys are 18''/8J/ET45, so with 12mm spacers on the rear made it ET33, so being wider and a lower offset meant I was getting terrible rubbing. I've only got 5mm on the rear now so offset is ET45 and ET40 which does the job (may get 2/3mm on the front) and should be fine for when the coilies get fitted.
Gavin I'm not sure how far you're dropped on the AP's but I can see from the picture that you've got Rotors, are these the S3 Rotors or are they from another Audi? The dimensions vary depending on model which is why I ask. Providing that you have the S3 Rotors which are 18''/7.5J/ET54, then 10mm on the front and 12mm on the rear will be ideal being lowered, this will make your offset ET44 & ET42 which isn't far off what I've got and I'm going to be dropping 30mm on the front and 20mm on the rear with AP coilovers and shouldn't experience any rubbing. Make sure to remove the rear arch screws as well if you haven't already. Regardless of the brand you go for, make sure that they're hub centric spacers and that the extended bolts (around 40mm) are Radius (not Tapered) as this is the type Audi use on their stock alloys.