Senator(future aspirations?)welcome and congratulations on your upcoming graduation from law school. Be sure to study-up for the bar, of course. As for the surrounds, the QS8s are so outstanding that they are in my view the clear choice of those that you've listed.
The best "bang for the buck" in a center speaker would be a vertical unit identical or at least as similar as possible to the mains. The fine off-axis performance of the cc-590 and cc-690 is understandable, since they in effect are small vertical speakers handling the mid-range and treble, while flanking woofers handle the less directional bass. This was noted by the reviewer in the Epic 80 review now featured in the Axiom blog, where the extreme dispersion was the only area where the Paradigm center was considered to be superior. Again though, a regular vertical speaker is more cost-effective for such use.
