You'd get far better brake balance with the S3/R32 front and rear setup
But brake S3/R32 is the one pistons and this is 4 pistons
And . . . . it isn't simply the numbers of pistons, it is actually the surface area of the pistons - and that is governed by simple hydraulics. What diameter are your Brembo pistons? Furthermore, why is it that the standard RS4 on iron discs uses an 8 piston caliper up front, yet the ceramic brake option uses a much higher spec 6 piston caliper - with far higher braking performance over the stock setup. 
Secondly, the S3/R32 discs have a larger diameter than the Brembo BBK. Again, down to simple physics (and with other variables being equal), the larger 345mm S3/R32 discs will be more efficient than the 330mm Brembo discs.
Really?! I was considering the Brembos :embarassed: My Ed30 will be running around 350bhp pretty soon. Would you suggest going down the S3/R32 brake route or getting some monster 10-pot Tarox brakes like Hurdy has. Point is, I don't want to overdo it and waste a lot of ££££s for no real gain... Oh, brake weight is an important factor too - maybe I should go for the expensive ones if I can shed 20kg or thereabouts?
If you are talking purely on brake
performance, then the front OEM S3/R32 setup will be more efficient than the Brembo setup.

And with the OEM S3/R32 on all four corners, you will have a much better overall brake balance, particularly under hard braking.

I think a chap called NeilM who uses this site had that Brembo kit, and he really didn't rate them - infact he toasted them on a track day - so I guess that whilst they may be OK, I personally reckon they are more 'style' rather than 'substance'!

But if you are just going for looks, then the Brembos, AP Racing, or the Tarox 10-pots have it (if they suit your personal preferences).

In terms of weight - I don't fully know. I am aware that the standard S3/R32 anchors are known a touch heavy - but at the end of the day, they still 'deliver'. Regaring the AP Racing setup, from what I recall, RedRobin did state they were an improvement over stock, but by how much - I can't remember. Hurdy should know the weight of his lush Taroxes.
But I would advise some caution with the Brembos - yes, some Brembo setups can be superb - but others don't really deserve their badge. You really need to know what the Brembo caliper housings, AND the pistons are made of. Some Brembo calipers still use heavy cast iron pistons, yet OEM Ate calipers have been using alloy pistons for a while now. And those Brembo discs will not be any significantly lighter than stock.

Finally, Audi (just like Bugatti & Bentley - who use AP) are now slowly moving away from Brembo - and are starting to use Alcon calipers on the new RS6 with the ceramic option.
As a last comment, if you are really seriously considering weight reductions, then you really need to be looking at ceramic brakes - either from the Audi parts bin, or some truely awesome aftermarket ceramics from the highly regarded yet little known German firm MovIt -
www.MovIt.de.

HTH