Ok, maybe a poor choice of wording and assumptions!
The sound was dull, flat, lacking dynamics and enjoyment.
Changing the cable gave a similar improvement (not as much, let me just guess at, say, 50%-75%, indicating highly noticable) as going from using a pro's analog out to an ultra's analog out. I think you're quite aware of my entirely subjective opinion on that difference.
I'm assuming the pro's cable was picking up noise from the very, very close proximity to surrounding equipment, mains cables etc.
If cables are just cables, what else could it be?
An honest question. I'm quite intrigued to know why, but right now all I can say is that, to me and my unknowing family, it was a significant change for the better.
I'm also quite open to believing that for others, in their setup, it might make little to no difference, and I certainly wouldn't assert that they must be wrong just because it was better for me.