I agree with Alex's advice and I don't think the problem is in the speakers or wires, but in a receiver setting.
About speaker wearout, just for information, my EPI 100 speakers lasted from 1968 to about 1998, or 30 years. The speaker cone surrounds rotted out and that was the end. My brother's Boston Acoustics speakers did the same thing in about the same timeframe, but he got a repair kit and fixed them. So speakers do go bad over time, but I would say the timeframe is roughly 30 years. I also have a pair of Cambridge Soundworks Ensemble speakers which I bought about 1998 and they are still good in 2008, or 20 years. So based on previous experience I expect to get about 10 more years use out of them, unless they improved the surround materials over the years and then they might last longer.