Well, you've had lots of good suggestions, but those speakers must be closer to the back wall to get a balanced response. If you move them back to within about 10" of the wall you should notice tons of added bass. The problem will be that the bass will overwhelm the midrange. To get it right, no matter what speakers you get, you should seek out a Sumiko dealer (they sell Sonus Faber and Vienna Acoustic) and pay him or her to set up your speakers using the Sumiko Master Set system. I'll work.
Dave
Dave