So in my continual room tinkering, I decided to situate my GIK 244 panels, which were previously situated at the FRP on the wall behind my speakers, to absorb the side wall FRPs.
The result was NOT subtle. These were my initial impressions:
Imaging snapped into place like I've only heard when I toe in my Maggies like crazy and thus lose my soundstage. At the same time, I started hearing details I didn't know existed in my recordings.
The best part is that my wall 'o' diffusion (4' x 8' of GIK D1 panels) now works BEAUTIFULLY behind my Magnepan 3.6s. I get a beautiful ambience, holographic imaging, and a wonderfully deep and coherent soundstage.
This treatment hadn't occured to me yet, since my left sidewall is a giant sliding glass door with plastic blinds and my right sidewall empties out into my dining area. However, with the stands that I'll be soon needing from Glenn, I think my room will be nearly complete.

-- Nils