The rear speakers are not as important as the front 3. You may want to look at 1.8mk2's for the rears. My system is going to have 4 Contour 3.0 and a T2.1 center. I think you will be just fine with almost any Dyn speakers for rear surrounds.
Rear speaker choices will depend a lot on placement. If you have to place them against a wall, you will most likely have to plug the rear port so it will not be boomy. So that will automatica change the tonal balance of book shelve type Dynaudio speaker by a lot. Might not be worth spending so much money. Even a pair of Dynaudio Audience 42W with front port will sound better.