Are you sure it's the speakers and not the sound card?
Is it aftermarket sound card or is it on the MB?
The 5 speaker system is hooked directly up to a Mac tower (an old G5 dual 2.5), so there's no sound card. However the subwoofer acts as the amp for the system since everything hooks up to it.
The other one is actually hooked up as an iPod speaker system ... iPod mount, 2 speakers + sub. My bad in not being more clearer on this system.
BTW, I find it interesting that both systems are made by Klipsch ... if that helps. Needless to say I don't think I'll be getting anything from them any longer.