It's generally a concesus that in an AWD system, you gotta have te same tires. This makes sure you got the same rolling diameter, same "bite pattern" and balaced weight on all corners. Some people will tell you that you don't. This applies now but down the line, say 15K miles, you'll have tires that had worn more and bald due to the different tire compounds. a 400 treadwear tire will outlast a 180 treadwear tire. One tire will be bigger AND heavier than the other.
Get a cheap set of Kumhos 711, they are 99/tire at Tirerack. It's better to spend more now in tires (400 bucks) than to spend more on a burnt center differential. Parts and labor for this will cost over a grand or two.
The cost of owning an AWD.
But hey, they are fun and really a different breed of cars.