Moving your speakers closer to the back wall will ad some boundary reinforcement to the low end. But you could muck up the low mids and imaging. The better solution is to move the listening position so that you are sitting as close to the back wall as possible. Antinodes (the part of the waveform with the highest amount of displacement) occur at room boundaries. As long as you sit with your head no further than 1 1/4 feet from the back wall, the bass will be at a higher amplitude, and the mid to high frequency reflections from the back wall will be so short, that your brain won't be able to distinguish them from the direct sound. If you want more info I think AudioPhysics has some info on their website regarding this monitoring scheme.
you'll get much more of an effect (you can expect ± 10dB/spl below 200Hz in some rooms) with speaker/listening position placement than you ever will with cables or electronics (other than an EQ). Save your money, take a little time, and if that doesn't work, then think about altering your equipment.