Couldn't tell you the driver difference off the top of my head, but the Contours are a far superior speaker in my opinion. I thought the Audience speakers were completely pedestrian in terms of depth, stage, imaging and detail. The only pity is the Contours are near four times the price. (Guess you should get something for the higher price.)
That said, I ended up with a set of Spendors which had the characteristics I liked in the Contours but for substantially less. (Still more than the Audience 72's.)