Greg, is the ceiling high enough that you could use an Axiom full-metal-ceiling-bracket and continue to use QS8's? I'm SO fond of the QS8's that it is difficult for me to imagine using other surrounds. Are you sure you can't find a way to mount them on the wall somehow?
If you're REALLY stuck with the round in-ceiling type, I'm not sure it makes a lot of sense to overspend. I am intrigued by the Mirage omnisat in-ceiling models; it seems like they would be fairly enveloping. I have traditional Mirage inwalls and also the small omnisats and I like them both very much.
We are a whole community of "that guy" - StPatGuy