First of i don't know if this is a tooltip error, or something but however it shows that i do in fact get extra crit chance, not 100% if it comes up in the math. On wards.
First you will require Darkmoon Card:Greatness. Not to sure if this works with all 3 of them but i know it works with the +90 STR one.
Secondly you will need the mirror of truth, (is the trinket i'm using after further testing i assume it works with trinkets that have "Equip: Improves Critical Strike Rating by X"
The process is quite simple as you can see in this screen shot my crit is 9.81%
By simply moving the Mirror of Truth on to the Darkmoon Card:Greatness, you can see the 2ish% increase in my crit chance.
Again i am not sure if this is just a graphical tooltip glitch, but it seems like its working. I reloaded UI it was the same thing. I even went naked to test it same thing. I tried different trinkets with improving crit rating still good. Now just to test the numbers. The things needed to get this benefit sort of hard to get but good luckEnjoy! Be sure to move the X trinket on to the Darkmoon card otherwise the crit will drop.