Diffusion vs. Sound Absorption views

whitestix, what you have are dipoles. Dipoles radiate in a figure 8 pattern. Very little energy goes to the sides. This actually makes them easier to deal with acoustically because there is only one primary reflection and that is off the front wall. For every foot your speakers are away from the front wall you can add 0.2 millisec to the delay. If your speakers are 3 feet from the wall that would be a delay of 0.6 millisec. This is to fast to be perceived as an echo. All frequencies are not reflected equally. This and the slight delay ruin your image. Diffusing the sound just makes things worse creating more reflections. You want to diminish the volume of the first reflection by absorbing as much as you can in the mid range and treble. Using double sided carpet tape attach two rows of these tiles from floor to ceiling directly behind the speaker. You can alternate the tiles making a nice pattern.
https://www.parts-express.com/sonic-barrier-fwp122-studio-acoustic-foam-wedge-panel-12-x-12-x-2-black-12-pack--260-547
It is an inexpensive thing to do and you will notice that your image sharpens right up. In most cases that is all you need to do. You might notice a slight change in frequency respond with less treble. In most cases this sounds more natural but the big improvement will be in the imaging.

Sir,
Great advice, which I think is pretty much where I am now -- all absorption.  Maybe I could send you a PM and somehow get you a photo of my living room for your opinion.  Thanks, Mark

No problem,

Mike

Diffusion actually reduces the strength of reflections off of the front wall, behind the speakers. QDR diffusers placed vertically will reflect out horizontally into the room and most QDR's need at least 6ft between them and the listener to fully form a diffused sound field. If a QDR is enhancing reflections vs a bare sheetrock wall, you probably don't have them set up correctly.  All diffusers absorb some of the reflected energy, as well.