S4 brakes

[reserves]

Thanks for the reply guys.

I was under the impression that as I had the facelift B5 calipers there was an option to use the B6 brakes without changing my calipers?

[tdiquattro]

There are two parts to the brakes, the discs and the calipers,
The changes between cars mean the discs are
- larger or smaller diameter and different swept areas (the part the pads touch is different widths).
- The discs "offset" also changes this is how far the disc sticks out, ie if it is closer inside the wheel or further out.
- they are bigger so the wheels need to be larger to clear them

The changes in calipers mean,
- the mounting holes are in a different place
- the pads are bigger/smaller
-they are bigger so stick out further and the wheels need to be a different shape to clear them (this can show up only with new thick pads)
- The number and size of the pistons in the calipers are different, there is some discussion as to the master cylinder piston (connected to the brake pedal) being too small for some setups.

So your original question has many answers! and it is difficult to cover every option in one thread, it is best to search the forums and see what choices are out there, some are more worthwhile and successful than others.
Even a sticky with all the possible brake upgrades would probably get over complicated.

Then there is a whole other world of pad manufacturers/compounds and groved drilled/cast hole discs !!