Do you get generally good bass if you plug in a headset? Or have you used other speakers that had good bass?
I looked at the manual for this and the only thing I see is the bass adjustment on the speaker systems control pad. It says to set the Equalizer in the media players for Off or Flat, in the troubleshooting section.
If you still do not have enough bass, and it is properly cabled and the bass unit sitting on the floor, it would appear it has a hardware problem.