I would recommend two things: Set up the speakers and your listening position EXACTLY (within an inch!) of what you get when following this guidance:
http://www.cardas.com/content.php?area=insights&content_id=26&pagestring=Room+Setup
The other is to experiment with super cheap bass trapping. Go to HD / Lowes / etc and buy four rolls of insulation. Stack them two high and put them in the rear corners. This should improve the bass response noticeably.
http://www.cardas.com/content.php?area=insights&content_id=26&pagestring=Room+Setup
The other is to experiment with super cheap bass trapping. Go to HD / Lowes / etc and buy four rolls of insulation. Stack them two high and put them in the rear corners. This should improve the bass response noticeably.