I'm assuming the speakers are broken in. If that's the case, I would suggest that you fix the problem instead of buying cables. Using cables to fix a problem like this almost never works. You should be able to get your system sounding good with basic, inexpensive cables first. If you can't do that, the problem, most likely, lies elsewhere.
I see only 2 solutions here. The first is to find out what component(s) are the root of the problem, and replace them now. The 2nd way is to buy cables now and then find out what component(s) are the root of the problem, and replace them later.
I see only 2 solutions here. The first is to find out what component(s) are the root of the problem, and replace them now. The 2nd way is to buy cables now and then find out what component(s) are the root of the problem, and replace them later.