Unless you're absolutely locked into to buying Brembo, you might think about the Stoptech Stage 2 brake kit which gets you everything you need for a brake overhaul. It is described as follows on the Stoptech website:

Stage 2 drilled brake upgrade kit for 2000-2004 BMW X5 with solid rear rotors. Includes front and rear Axxis Ultimate brake pads, front and rear StopTech stainless steel brake lines, three 500mL bottles of Motul RBF600 DOT 4 synthetic brake fluid, and pair of front and rear stock sized StopTech cross-drilled brake rotors. FITS STOCK CALIPERS.

$719 for the entire kit, MSRP. You might find it cheaper if you shop around. The next step up would be a big brake kit from one of the major aftermarket companies (Brembo, Stoptech, Rotora, etc.).

There is info regarding Stoptech available on the Zeckenhausen website. Stoptech makes some excellent and very track-worthy products.