Dave,
I second the QS8 comments. Nothing can make it sound like bullets are whizzing past and over your head like the 8's.

Excellent...
So, QS8s will likely be next, then an M2 for the center.
-or, the other way around....ah, choices...stupid budget!!!

Considering how close together the mains are I think you should get the Q's first and stick with a phantom center.

I actually already have a center, so I will just use it for now. My fronts will be about 9 feet apart, by the way.
Does anyone see a significant problem with having the center on a shelf right above the television? If I were to wall mount my TV, I could put the center on my equipment/TV stand, then it will be at the same height as the front speakers-that would be ideal of course. I guess I can certainly 'test' the center in both positions and find out for myself...

You answered your own question, decide for yourself

I ran my center over my TV and it was equally as good as having it lower, possibly even better as the 150 seems to sound a little better, at least to my ears, the farther away it is.

A pic of my old set up for reference: