I also use Dspeaker (orig.) on my subs, but more recently have experimented with some 2'x4'x6" insulation (rock wool type) that I put between some 1/2" pvc as a cage/ holder so that I can move them around without having them flop over. That also helped smooth out the bass a bit, but too much in the corner can deaden the sound so you have to be careful.
But I still stand by my DIY Shakti Hallographs as having a very good affect on the soundstaging and image focus. Because I put them on lazy susans, I can pivot them where they sit right behind the speakers--there are some recordings that are a bit "in your face" meaning I would want to add some room ambience/reflection via the Hallographs, so I point them at the reflection points on the side walls. There are other recordings that sound too diffuse, and positioning the Hallographs to toe inwards usually does the trick--so much depends on the recording.
Also, while messing around with the cheap version of the DIY, I made a few and one ended up on a side wall more as a diffuser and I have also been using one two feet off the ground right between both speakers. I have tried it with and without one, and right now I prefer it with. YMMV!