Replacing with Better speakers will make 10x the amount of difference that replacing some cable will, it is never worth the outlay as the speakers you have only have the capability they have, their capability cannot be exceeded no matter what cable you have. They can only perform better by getting new speakers or possibly new amp, but even changing the amp is debateable as it just changes the tonality of the sound the speaker is producing.
Im sorry but no matter what companies claim they do to their fancy cable, just basic oxygen free stuff that's thick enough to carry the signal will do. Never worth spending loads on cable.