I found dialing the bass down on the EQ helps with certain music types. I also find it to be muddier at lower volumes, and better integrated at higher volumes. It does produce tones seemingly all the way down to 20hz, which is impressive for the size of the subs, but it seems to struggle with clarity in the bass tones at lower volume levels. All said, though, the audio quality at moderate or high volume levels is better than any other factory system I've heard, even up into the six figure range.
The only other thing that might be doable is to plug or 'soft plug' some of the sub ports, assuming the subs are ported, but you'd have to take it apart to figure that out and test it.