Since you're desperate for an answer, I'll give you mine, but I've never tried
the Korg n364 so keep that in mind.
I did try the Proteus and I was very excited about it when I heard about it. When I saw it at my local Guitar Center I couldn't wait to start playing with it. I was deeply dissapointed. The sounds weren't up to the standard that I expect from E-mu. The claim was that they packed in the power of many of their rack mounted modules (which I like very much), but I couldn't coax such sounds from this unit. Furthermore, the interface makes Yamaha synths look easy by comparison. Just gettting around on this thing was hit and miss, where it should have been instinctual.
Now, as I said, I've never tried the Korg n364 (hence why you got no response from me before about this), but I find that Korg as a keyboard manufacturer is consistant when it comes to good quality. Look at the Karma, Triton, CX-3 or any of thier less expensive synths or digital pianos and you'll see what I mean.
As far as I know the Proteus is E-mu's first forray into keyboard design since the Emulator (I may be wrong about that, but they certainly don't produce a plethora of keyboard units).
So, I would recommend Korg over the Proteus based on what I've said above. Still, the Korg n364 might suck like a Hoover, so take what I say for what it is worth.
Carl