I've gone against a LOT of Darius' top as Xin... (Why do people love him so much?) It's pretty equal footing pre-6, once he hits 6 you can't 1v1 unless you already got ahead of him, If you get a gank when he hits 6 and can walk away with a kill and no deaths, you should just stomp on him the rest of the match
It also really depends what you build on xin, I usually just go full on bruiser
Xin has 1 method if initiating the fights, besides having Darius initiate it for you, and that blows his means of escaping.
Blow your E initiating, and Darius will just use his armour pen on-hit move, then AA you until you try to leave, when you do, grab, more AA. Pre-6 you'll lose this trade. Post-6 you'll die from the dunk following the last AA.
Not to mention he can harass you in lane, and you can't really do it back without taking some damage. --- Signature
Xin wins every trade pre-6 unless you start the trade with all the bleed stacks on you, every Darius you face will never realize that. --- "Whats the penalty for dodging in ranked?" "Phreak comes to your house and punches your screen."