From the picture, maybe you need some type of wall treatment to absorb sound. I don't know what is behind the camera but if it's the same as what's in view, you might have an acoustic problem. Try to hang something on the walls that will not reflect sound. Also the same goes for the floor. Bare walls and floors are a no-no, and don't overlook the windows, curtains on those. Next time you go to a movie theater look at their walls and floors, lots of sound absorbing materials.
Speaker placement is another factor. try moving the cabinet that holds the electronics out from the wall and placing the speakers closer to the wall. But keep the speakers about 8 to 12 inches from the wall if possible. I see the room is small but do what you can. Have you tried adjusting the bass and treble in the receiver, that might help. I see in the picture that you do not have a center speaker and that you are relying on the 4B completely, the 4B is a good speaker, but I think it's primarily a satellite speaker. Therefore it might not give you the performance you want. You might want to consider the 5B. Sorry thats another $95 each. Or maybe even getting the 4C to go along with the 4B's, thats $160.
There is an Aperion thread http://www.avsforum.com/avs-vb/showthread.php?t=772081
Lots of help there also.