I don't have (any) experience, but I would say the cables are not the culprit. It must be the tweeter, in this case (since you have them/tweeters - I'm just guessing like a said) a bad job in xover design. You probably want a more relaxed sound with an attenuation on highs of 1 or 2 dB's. The type of room/furniture and distance to speakers can also affect the overall.