Dipole surrounds
I also have the 100s, but with the CC-470 and ADP-470 dipole surrounds. Although I really like them, and everyone thinks they sound superb, upon reflection, I think I might suggest you go with the 20s for rear surrounds. Although the ADP-470s sound great, I feel that one tends to lose a bit of the directional imaging that the 20s would probably provide. I hope to, at some point, add mid point surrounds in order to achiever true 7.1, and at that point, I think I would move the ADP-470s to that task, at which I believe they would be grand....
In the meantime, I'm simply continuing to enjoy them as is.
Pat