musicfile, I have a smaller room that I use Michael Green Roomtunes in. I DON'T have the type of investment that you have but.... diffusion has helped me ALOT thru the use of 48" standers. Now I use Apogee Slant 6 speakers and have them set up much like you myself, here are acouple of tricks tthat have helped me as I've continued to adjust thru the years. With free standers I am able to adjust more freely but I use the diffusion side of the panels (3) on the front wall behind the speakers and (1) on the rear wall. Small (and I do mean small!) adjustments to angles you hear a big difference with (as small as 1/16"). My panels are off set in distances as well with 2 forming a corner and 1 in the corner of the front wall but not equal from the placement behind the L & R speakers. My 3rd panel is only 18" away from the rear wall yet 5' away from the corner and 2.5' from perpindicular with my listening chair. I also use 4 Corner Tunes to kill the slap echo. I use a rediculously cheap tuning control adapted from Marigo's Tuning Dots that work eerily well! When I had gone to the sight (Marigo) it told you how & where to place dots for tuning of the speakers. Using U.S. Quarters (for me) on the base of the speakers I adjust the distance from the OUTSIDE EDGE to adjust the focus and width of the presentation and again TINY ADJUSTMENTS make huge differences. Marigo suggested a starting point of 1/2" from the outside corners inward and then adjusting from there. For my $1.50 investment I have blind tested many people in query of the differences and in all cases THEY COULD HEAR THEM, either the staging collasped or was too diffused and lacked the definition clarity, but get it right and it saves hours worth of time and it's super easy adjusting as well. I hope this also helps with your search and as well pay attention to vibration control with your rig even if on a concrete floor or base becuse it will pay dividends like you haven't heard as well. Good Luck :)