your comparing two COMPLETELY DIFFERENT cars and AWD systems.
The XI awd system is known for being unreliable, very over complicated expensive, and its computer controlled. there is sooooo much more to go wrong, and it all costs a shit ton more.
the ix's awd system is extremely simple, completely mechanical. and compared to other awd systems, cheap.
the transfer cases are known to be somewhat weak, usually because of neglect. all that means is you have to find one in good working order. which can still be found for cheap as hell. and if you do fuck up the transfer case its 1000 dollars that you will never have to spend again. my friends ix has 220,000 miles, stock tranny and awd system, he's got a built m20 with something like 200-215 at the wheels, he launches the thing all the time, and beats the crap out of it. he had the transfer case checked out like 2 months ago and it was working perfectly. the transfer case is literally the only iffy part on the car, and even thats only 1000 dollars for a new one, less for a rebuild.
other than that the car is reliable as hell, parts are sooooo much cheaper than an e46. i know alot of people with e30's one's got over 300,000 miles on stock everything, he's owned the car for like 5 years and done nothing but regular oil changes and crap.
in my experience e30's are alot more reliable than subaru's. ive seen alot of both in my friends shop, and its almost always the subaru's that are in for repair.
but yeah, the 330xi and the 325ix have literally nothing in common except the 3 in the name. and they are complete opposites when it comes to reliability.