The big brake kit usually comes with
1) 2,3,4-piston calipers (as opposed for the single piston design of the stockers)
2) high performance brake pads (usually grip better when heated up)
3) larger rotors (to dissipate heat better, since the brakes are really a giant heat sink)
4) stainless steel brake lines (firmer brake pedal feel because the expansion of the stock rubber lines is no longer there)
Contrary to what most people think, cross drilled or slotted rotors do not reduce stopping distance. For track driving their ability to control outgassing might be advantageous, but for a vehicle like the Murano (or any other street car) it is just for looks (and its also less durable than a normal rotor). For the Murano I would forgo the fancy rotor and just go with a cryo treated "blank" rotor.
$2600 is a ridiculous price for just the front brakes.