Brake squeal is the high frequency vibration of the pads in the caliper at lower speeds. If the pads have a low tolerance in manufacture, then they will rattle in their slots. I have measured Redstuff against the Audi pads and found this to be so.
Regarding brake disc warp - think about it. A honeycomb of webs (the cooling vanes) separating two faces is going to take a lot of heat, and I mean a lot, to actually warp a disc. Disc warp is a term applied when there is feedback through the brake pedal giving the feeling that a disc is warped. In actual fact, the symptom is a product of incompatible friction material on the particular disc, especially where hard braking has been used. The incomaptibilty between these materials produces high spots.
I suspect that the general consensus of the fix might be that Redstuuf or Ferodo have a higher tolerance in manufacture of the backing plates and their compounds are more symapthetic to the disc casting.
All this is well documented and it is beyond belief that those in Audi will not recognise this and fix it. It is so simple, that I reckon a small team of R&D chaps could hack it in a day or two. I really cannot say the boffins behind the RS3 are boneheads as the car is genearlly top drawer, so I have to say, they are just boneheads..!