Which cable has most impact - IC, Spkr., power?

Definitely depends on the compatability of the equipment/cable link and the synergy between all of the equipment and cables. If you cannot establish a synergy between all of the cables, you will be changing cables frequently. Some people decide to change the equipment instead. I would focus on upgrading your speaker cables and build around them. If you build around the interconnects, it can be a lot more expensive to constantly be changing speaker cables. For me, speaker cables made the biggest noticeable change, which I feel also reduces the amount of noticeable change derived from the interconnects and power cables.

Shandorne's post makes a lot of sense but I have to agree with Joe also. Even assuming that one has the finest AC power and the perfectly constructed component, one would sense that one cable has a greater influence on sound than another cable. I am not an engineer, but are we saying that when one adds speaker cables, power cables or IC's to perfectly clean AC power and a perfectly built component, that their is no noticeable sonic change? If this is the case, than I have to believe that no component has ever or will be properly designed and perfect AC power does not exist. Since we haven't reached that point of perfection, It doesn't leave much choice but to pursue the pefection in another way. I suspect we are all going to be fussing with our cables and equipment for many moons to come.