Thread title updated to reflect the ongoing discussion.
As for ATH-M50LE vs A900X (Trying to recall from a week ago)
A few notable differences:
The M50LE's have more bass
The A900X's have much better...
I find the leakage bad if they're not being worn--otherwise they don't seem to leak much sound at all.
Also, I recently had a chance to compare them directly to the Beyerdynamic DT990 Pro's!
They sound very...