Call GIK Acoustics and ask them for help in selecting a product. You may decide on something completely different to meet your needs.
diffuser
can this be used as a diffuser on the wall behind the speakers?
https://www.worldmarket.com/product/mosaic-wood-panel-with-shelves.do?sortby=ourPicks
https://www.worldmarket.com/product/mosaic-wood-panel-with-shelves.do?sortby=ourPicks