I purchased a Denon X3800 this year, and though I love the amp, I HAVE found a tonne of cracking and popping with my subwoofer (Infinity PS-10) I purchased in 2003. The cable is about that old.
I've tried adjusting the crossover points, and that made a tiny bit of a difference. My understanding is that I should try replacing the cable.... And if that doesn't work, I need to look into whether the subwoofer will work with that amp.... Maybe they are mismatched? How would I tell if they are mismatched? If they ARE mismatched, how would I learn which subs match that amp?