You ask an excellent question, freediver. A few who have posted here touched on the technical reasons, but no one has given a clear and complete explanation. I can't either. But, there's no doubt that complex things are happening in cables that affect what we hear in a big way. My own system has 3 brands of high-end cable that work well for me, but there's no point in naming them because what works for you could be different. Here are the things to remember:
- Speaker cable interacts strongly with both speaker and amp. Get to know a dealer who sells both, because he will have experimented with lots of cables, and he'll know what works well. In my case, since both the speakers and monoblocs are by MBL, my dealer has lots of experience with what goes on both ends of the cable.
- Quality doesn't necessarily always increase with price.
- There is at least one prominent company out there (I won't say) that sells overpriced snake oil. You'll be able to figure out who it is if you pay close attention to their ads in TAS and Stereophile, as they use lots of pseudo-scientific words designed to make you think they have discovered magic.
- Interconnect is important also, but in my experience what's good with one brand of source / pre / amp is good with others. Once you choose a speaker cable, maybe a good experiment is to try the same manufacturer's interconnect.
- Trust your ears.
- A cable company that has a lending library can be your friend in this.
- After you've chosen speaker and interconnect cables, listen to power cords. I thought that was lunacy at first, but it's not, and now I have all that plus a power conditioner.