In the words of Albert Collins...

I ain't drunk. I'm just drinkin'.

ghost, it sounds like you have plenty of space behind the speakers (which was not evident to me from the pictures, because squirrels have poor depth-of-field perception in two-dimensions).

Honestly, I don't know if just some fabric on the wall will be "effective" or not. There are other folks around here who are more knowledgeable about room treatment implementation than I am.

I'm not sure which of our friends first posted the link to ATS Acoustics, but they seem to have the goods.

bibere usque ad hilaritatem