two way v. three way speakers


I recently heard some magico mini's at a friend's house. They sounded amazing. And they were 'only' a two way speakers, but they filled the room with amazing sound. So now I wonder, what does the additional driver add, especially when it is the same size as the second driver. For example, the SF Olympica III's have two drivers of the same size. I know that third driver adds a lot to the price, but what does it sonically? Thank you all in advance.
elegal
I used to have 3-ways with two 61/2 bass drivers and an identical mid driver. Now, I have a single 51/2 driver in a transmission line speaker with a parallel sub. The first ones were 91db and the current ones are 95db. When I go to my dealers showroom and listen to the ones I used to own, I can hear the crossovers and interrupts the musical enjoyment. Once you go crossoverless, it's hard to listen to more filters.