Originally Posted by
LAWPRE
It is not the magnitude but the SOURCE that decides what does or does not stack. A +6 from sources A, B, C will get you +18. However, +6 from sources A, A, C will get you +12 and +6 from C, C and C will get you +6. There is one thing that will override this - epic items (specifically exceptional bonuses) from the same two sources with add.
I believe that stat (Dex in this case), Magic, Armor, Shield, Force, Tomes and Natural are the different basic item codes. So, +40 (as Tomes will add +1 to AC for every 2 points) to AC should not be that difficult and this is still true for a Monk (as Wis and Dex count for them).