Strangely enough, when I tried using an old QED interconnect I had kicking about as a 'stand-in' digital interconnect, I found real problems with the sound. Moving to a dedicated (but inexpensive) digital cable made a big difference.
Shouldn't have, but did. I'm still fairly cable skeptic these days, though I have heard differences in certain cables, most notably things like the Anticables and the NVA cables. Still reckon that worrying about cables before the room is sorted (which mine isn't, tbh) is like putting an elastoplast on a broken leg... not that my room issues are that serious mind you...