Let me start with the obvious...your room acoustics suck but you are halfway to better sound now that you have taken the time to understand where the nodes are. First thing to do is spend a couple of weeks reading up on acoustical treatments. Once you have developed your understanding I would suggest you concentrate on basstraps in the corners which will have the most impact on smoothing your peaks and nulls. Next experiment with panels athe prime and secondary reflection points from your main speakers. Finally consider a good equalizer. The road to improved room acoustics is a long one but the most significant thing you can do to get better sound...moreso than buying new equipment.
