You also need to consider the size of the caliper piston compared to the master cylinder. If the Brembos you are looking at have significantly larger piston volume it will mean that you'll need to push the brake pedal further to achieve the same braking effect, leading to a loss of feel.
You will also potentially be restricted in terms of what pads you can get, and you may have to have custom discs made depending upon the thickness of the standard 7 series discs.
Someone Audisport.net has just been through a load of hassle with some 'cheap' Brembos he got which came off an Alfa which Bill helped him out with working out exactly what he had bought and what pads fitted.
As Mr D says, anything is possible, however you could end up spending a fortune in the long run.