Triggers - Item Sets

[Xeridanus]

I'm making a melee map and was wondering if anybody could help me. I need a set of five items to interact with each other. When a hero has two or more items of the set they co-operate and become more powerful except for one of the set which only makes the others more powerful, doesn't become more powerful itself. If you've played Diablo II you'll know what I mean.

Thanks in Advance