JPump

Changed all 4 brake pads on the car this weekend and thought I'd share what i learned based on some questions I've seen.
OEM Pads - Didn't go to Audi but bought some Brembo pads from ECP. Front pads were 1ZA and rear were 2EJ, this is needed for fitment when buying online. 4 Pads and 2 wear sensors for £150ish.
Front Pads
Do not be tempted to go for the ribbed bolt on the top of the caliper, this is a proprietary fitting used to stop you trying to change pads. There are 2x21mm hex on the back that allow the caliper to be removed. The brake line into the caliper will need to be removed and so brake bleeding will be required on completion. Be prepared for brake fluid to go everywhere, especially when pushing the pistons back into the caliper with the brake line removed. The retaining springs will need to be removed from the top of the caliper before the pads slide out. The rest is all fairly straightforward for a pad change.
Rear Pads
2 bolts on the back of each caliper, fairly simple single-single piston calipers. Main thing to note is you need to put the brakes into 'Service Mode' in order to fully retract the parking brake, taking the parking brake off inside the car is not enough. To do this you will need a service tool/VCDS. Be sure to remove from 'Service Mode' when done which will reactivate the parking brake. You may have fault codes from the parking brake motors being disconnected.

Hope this helps as it can cost an arm and a leg to get done and really isn't too hard. Took about 2 hours on the driveway.

RickNY

Not sure if you saw these prior to your job, but these two links below are pretty helpful

There is a very good DIY writeup at AZ: - B9 S4 / S5 DIY brake pad and rotor change...
There is also two good videos here at AW: Video Tutorials of Replacing Brake Pads and Rotors for Audi S4 B9

JPump

Nope didn't see them, very good and would've made it quicker. Cheers