The advantage of monoblocks is being able to keep the amps very near the speakers so as to keep the speaker cable as short as possible. The lower the impedance of the speaker the more important this becomes- really helps when you want to get bass impact and greater vocal definition!
Maggies allow you to place the amp right behind the speaker so its possible to run speaker cables that are only 6-8 inches in length. I've seen this transform the performance of the system- in particular when tube amplifiers are involved.