I have not used Echo Busters personally, but I don't think they will be very effective at reducing bass mode problems in your room. The standard Echo Buster panels will have no effect on bass. The "Bass Buster", designed to fit into the corners, covers too little wall area in your room to have a significant effect. You'd be much better off building membrane bass absorbers mounted on the wall - check out this site as an example.
http://www.customaudio.freeserve.co.uk/articles/membranes.html
If you find that you still need some equalization, check out the Rane PE-17. This is a five band parametric equalizer where all five bands can be applied to the bass region, and is available for about $400.
http://www.customaudio.freeserve.co.uk/articles/membranes.html
If you find that you still need some equalization, check out the Rane PE-17. This is a five band parametric equalizer where all five bands can be applied to the bass region, and is available for about $400.