My initial 7.1 rear surround set-up was four Acoustic Energy Aegis Ones.
I made special stands for the rears to get them up higher than the side surrounds, and then had to angle them down because the rear effects sounded like they were coming from the front (I think the sound was bouncing back from the screen)
I had also bought some Eltax HT2 Bi-polar speakers to experiment with for the side surrounds.
The result (for me) is that bi-poles at the sides sound too indistict and vague, but I tried them in the place of the rears, and they give the rear effects more presence. I never mistake the rear sounds coming from te fronts now either.
When DPL was the best surround we had, many said that bi or di-poles were best for the surround channel because of the limited bandwidth, and the fact that they were mono. I think exactly the same reasoning applies for the rear channel as well.
It's still early days, but I currently prefer direct radiators at the sides, and bi-poles at the rear. The bi-poles are smaller than the AE Ones, and are wall mountable. There are better sounding bi/di-poles out there, so it may be worth looking at what's available if you decide to give them a try. Of course a demo would be the only way to tell.
HTH
Gary.