Mike, I don't have any direct experience with the QS4's, and I certainly don't think they are shabby. My concern is that you already said you intended to use QS8's on the sides and that you might hear the same sort of timbre differences between the QS4 and QS8 that people perceive between the M22 and M3, for example.
I think running three speakers in parallel would give you a 2 ohm load. While I envy your HK, I'm still not sold on that idea.
Frankly, I don't think mounting the QS8's flush on the pitch sounds like a bad idea at all. I mean really, it is a loft area so you're not exacly in a laboratory anyway.
If you are sitting relatively close to the screen and you can place the mains reasonably close together, a phantom center might just work better than you think. It's worth a shot, anyway.
Good luck. I've always loved the pictures of your home that you shared some time ago; they make the visualizations of your questions very rich for me.
Happy New Year.
