HAVE CABLES EVER TAKEN YOUR SYSTEM FROM SOUNDING JUST OK TO SOUNDING GREAT? Experiences ?

The subtlest of subtleties, this is the gateway to all mysteries.

ok.. so, I've been down this road a bit and my answer is a little nuanced:

1. There are technical considerations involved in cables that will absolutely make a difference in sound. For example, I got a new phonostage and ordered a new RCA cable for it. The phonostage arrived about 2 weeks before the cable, so I used a spare 10ft RCA I had lying around to test out my new piece of gear. I instantly noticed a thick veil over the sound like a wool blanket was draped over the speakers. Of course, I thought the problem was the new phonostage (this is after I broke it in for the recommended 30 hours). I was going back and forth with the manufacturer and looking at spending $$$ on NOS tubes to fix the sound when someone here on Agon suggested that it seemed like an impedance problem and that I should check the signal chain to make sure impedances were matched across the cart, phonostage and pre-amp. I ran this by the manufacturer and they said, "the impedance pairing across your gear is fine, but what cable are you using?" When I told them, they instantly said, "Oh! That's your problem right there!" Sure enough, once I swapped that super long cable out for the new one I ordered, the problem disappeared!! So, in conclusion: did swapping the cable out make a "dramatic" difference? Yes! Was it because of all of the nonsense claims by cable manufacturers about the special materials and proprietary shielding they use? Absolutely not. The improvement that @rennieboy mentioned with his Vandersteens is likely due to better impedance matching and not the "higher quality" of super expensive cables. 

2. Cheap cables can cause issues like RF interference and bad connections. So swapping them out will make a dramatic difference. However, once you have a cable that is: 1. Well constructed 2. Well shielded and 3. Well terminated, you will get little to no improvement in sound quality by "upgrading" to super expensive cables. This experiment has been tried time and time again. There have been multiple blind listening tests. Electrical engineer audiophiles have analyzed this to death with frequency response measurements. And on and on and on. The difference between a cheap $5 RCA and a ~$100 RCA can be moderate to substantial. The difference between a ~$100 RCA and a $10,000 RCA is little to none at all (most of the improvement will be WELL below the audible range of humans). 

Just my 2 cents... good luck!

Calvinj , I think Nordost does do cable demo on the show from low price to their expensive cables.