I am pretty sure that the MA900 is built solidly. It's probably less fragile than most headphones just because it's so light and flexible; if it were dropped it would absorb shock easily. All the pieces seem to fit together well and fit and finish is up to Sony's usual standard for mid-fi gear.
I just doesn't FEEL nice. It feels flimsy. The Audio Technica cans feel marvellous in comparison.
I very much agree with this. The MA900 just feels too light and flimsy while the AD900x has some good weight while not being heavy at all. Its very solid. I'd be more afraid to drop the MA900 but idk exactly how sturdy it is.