The point is that i usually play xin more offensive that kind of offtank/support, that's why i take AS shoes. I also take madred cause it gives damages armor and AS, i've never really tried criticals with xin, i made infinity only in 1 game and i was so fed. Most of the games i'm around 15/5 with this way of playing but is said it, i do it only if i trust my tank, if i don't trust his abilities, i focus more on defensive items from beginning with Ninja Tabi or Mercury, Frozen Mallet and directly Phantom Dancer.
For trinity, i won't lie, most of the time i haven't time to finish it, so i don't really know if it is really effective on xin... i supposed that the hp, the AS, the MS and the passive ability should be great on xin, so i'll try to really try it and change it if it has no real use on xin...
I'll add some things in my build, making madred should be better when you have high hp ennemy champs like olaf or trundle. Sure that it's better to do Phage, Phantom, then finish frozen etc... I'll try it now.
Thx for the comment, i'll fix all these later =)

strange build for xin - can't see how bloodrazor or trinity would be ideal when you could be capitalizing on his attack speed with critical strike via Inifinity & Phantom - you certainly dont need the slow as you have the FM. Also couldnt recommend the berserker's when he already has tons of AS; Mercury's or maybe the Ninja Tabi would be much better choices. If you build Xin right he's going to get targeted first, and either of those can make all the difference.

Played a Xin a couple days ago that had a very similar build to yours, and he got stomped late game.