My left surround is hanging right in front of a window and you are right , it is not optimal but you can still acheive great sound. I think that the blinds actually help to act as a sort of diffuser- maybe a little-

Maybe you can wire them up and have someone hold them (or a couple of people) to give you an idea of where they would sound best? Or, depending upon how heavy or fragile the speakers are, temporarily attach them to the ceiling and experiment with placement. Once you cut those holes it's set in stone..well kind of. You can always fix it but what a job. :p

Let me know how you like the 990. I have never heard it but if it sounds anything like it's Uncle Sherwood you will be thrilled.

How are those bipolar speakers? Do you have a lot of room for the fronts? I have read that the placement on those is tricky. When I was hooking up my HT just as a dry run I had a Polk FX30 bipole/dipole speaker placed as my center (just checking the connections) and I actually really liked the effect. It sounded pretty neat.