ok here's my take on the X50, after spending about 20min playing on it at city this afternoon:
sounds:
firstly, only spent 20min cos it's very similar to the triton le and karma. recognised about 75% of the patches in there having either same name or same sound, or both, as those on my korg karma. there might be more similarities to the triton le which i am not as familiar with. couldn't see or hear the extra 32MB PCM (apparently X50 has 64MB PCM ROM). X50 owners please help to point out if i've missed out on any new material. i would like to go back and check them out.
keys and action:
similar to triton le. a bit more plasticky and cheap, like the way radium 61 feels plasticky and cheap. and keybed is spongy like the triton le, not thumpy-hard solid like the others such as karma, TR, extreme. while most players might not feel comfortable with it at the first few takes, i think it could potentially be something that grows into you if you play on it long enough. it can be pretty expressive if you use that sponginess to your advantage. i managed to attain a few glimpses of a greater degree of expressiveness which would usually be harder on say, my korg karma keybed.
navigation interface: korg has replaced the 4-way buttons with a 4-way joystick. feels a bit funny twitching a very un-ergonomic stumpy joystick instead of pressing a button. buttons are still faster, to me. LCD screen is smaller with finer pixels. but still large enough to be readable.
overall: not built with the tougher feel like the tritons. this one is the m-audio radium of korg. probably won't survive a fall off the keyboard stand. sound-wise, nothing new from korg with this one. just another triton under a different name and lower price bracket.