Markraz:
Interesting your idea of bringing your friends speakers for comparison, that could be an "ear opener" experience.....
As you describe the enhanced bass response your system has and looking again at the pics, just for kicks would like to suggest that you try moving the speakers 2 feet away from the rear wall and compare bass response.
Additional suggestion could be to place a blanket on the rear wall behind the stand for getting a small glimpse of gains you can get.