My honest answer is, some people can train themselves to hear through a lot of crap and can hear a difference with mediocre systems. I cannot, so I have to have a very good room first, then everything else follows, and then I end up caring about cables a lot less than when I started.
How good does my system have to be to realize an improvement with cables?
I've heard the difference power cables and interconnect cables in a highly resolving system so that's not the question. $200 for cables on a $500 DAC doesn't make sense to me. Wouldn't that $200 be better spent on a better component? At what point is an expensive cable the best choice? Spending $500 on a $15,000 DAC does make sense as the transparency and resolution of the component could be better realized with a better signal / power source.
My question is what's the percentage of the overall component's cost should be the cabling and at what point should it even be considered?
Or put a different way How would you know if your cables are your weakest link?