it's not a "trusty system" if it fails you after only a couple of years. speakers are not supposed to break that fast. if it's getting crackly you have listened to them too loud (or there's not enough headroom to begin with), wich basicly means you DON'T want to get a system with similiar wattage; you obviously need more wattage. your old system had only a 56W subwoofer, wich is weak as hell. low frequencies need more juice if you want deeper sound, and you obviously do want it if you are looking for 5.1 system.
the system that FelipeInsidie recommended is atleast an improvement. you might want to consider it. 150W subwoofer would be solid for desktop use.