Based on experience with my own cables in customer environments, the IC's make the biggest difference, followed by the speaker cables. However, this really depends on the IC's. My IC's have extremely low capacitance (3.8 pF/foot), so they make a huge difference. It is fairly easy to make a good-performing speaker cable, but more difficult to make a good-performing IC. Many manufacturers therefore have better speaker cables than IC's, even at the same price levels and so they probably will make a bigger difference.
Biggest Improvement Speaker Cable Or Interconnects
What do you guys think is the biggest improvement in a system, speaker cable or interconnects?