Oh, I did not know the A900X was aluminum.
The AD700 is plastic while the AD900 is magnesium, and the difference in sound is easily worth the price. From what I've heard regarding the A700 vs A900 (not the "X" versions), they were pretty close in sound. So, I'm not entirely sure which I'll get. Amazon's got to get the A900X back in stock, first, before I even start deciding. But like I said, if the difference is a similar improvement the AD700 to the AD900 saw, I'm all in. Guess we'll never know though, since nobody has both. (I think there may be like a whole two people than own the A700X).