Brake ducts from a Phaeton may have helped most, since they turned high speed air into cooling for the brakes. But that's just a guess. Other mods were stainless steel brake lines, Pagid blue pads, and brake fluid with higher temperature tolerance. The total of $2721 also included a new set of stock front rotors, which were the priciest part at around $1700. Put another way, if I already had good front rotors, the total cost of my mods would have been little more than $1K.
All mods were done by Suncoast Motorsports in Sarasota just before Daytona, which involved nine sessions of 25 min each over three consecutive days. Have made no changes since then (early Dec) and rotors still look good.
At the link, scroll down to the two entries made on Dec 24 by JAXRS6 (that's me on the rs6.com forum).
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Current: 03 RS6 - Mugello blue, carbon fiber, solar package
Previous includes: 05 Crossfire SRT6, 00 S4, 98 A4, 86 Buick Regal turbo, 75 BMW 530i, 7? Lotus Elite, 72 Jaguar XJ6, 71 Audi 100LS, 69 Firebird 400 convertible, 68 Dodge Charger, 52 Triumph TR2