What are the dif. between Virt. Dyn. Revelation versions??

Guys - I have a  new to me pair of Virtual Dynamics  Revelation Signature RCA's- looking to pick up another pair but notice that their is the Revelation,Revelation 2.0 and Revelation Signature- Can someone tell me what the difference between these different versions are and which one is the best-
Also are these cables directional??