How high end must your system be...

...for you to be able to notice the differences different cables will make. I've always said that I have ears of tin until a friend of mine came to my house and said that my system was just not high end enough to be able to hear the differences different cable will make. My system isn't the newest but it wasn't that cheap. My system is valued at several thousand dollars and I don't think I have anything in my system that you can find at just any audio store.

So, how high?