Its been a while since I dealt with those two boards, but if my memory serves me correctly :
-N264 has RPPR were X2 does not
-X2 can load PCM sound cards (is that what they are called?), were the N264 does not have card slot.
-N264 and X2 use the same sound engine, but N264 has more sounds in it I believe.
Overall I would say go for the N264, but as Arbaz said Triton LE (compared to the new price of N264) is a better deal, the Triton is all together on a higher scale rank than both N and X, but if your deal is on a used board, and u r on a limited budget, the maybe you don't want to consider the Triton LE. I think its going for around $1200 new right now???
Good luck