Don't spend a penny on new equipment or cables until you have verified your set up is not the problem.
It could be as simple as the speakers, subs, or your listening seat are in a null. It could be that there are phase issues between the mains and subs creating a cancellation.
Try turning the subs off and listening to just the mains. Does the problem persist or is it reduced? Try moving the mains both forward and listen, then back and then listen.
Try playing the subs only, and see if the problem persists. Try moving the subs out to about halfway down the side walls.
Try moving your listening seat forward or back in the room, both with and without the subs. How does the bass quantity and quality change?
There are too many things that can be tried for free to diagnose what is going on. Randomly buying cables and components is more likely to result in a lot of money being spent and still not getting good results. Your components should have more than satisfactory bass quantity and quality when properly positioned and set up in the room.