Dave is absolutely right; in systems with enough finesse to reproduce sound delicately the changes between jumpers and wiring is detectable. Just yesterday I replaced the power cord on my Rega Saturn cdp with an MIT Oracle and the difference was easily discernable.
I don't spend a lot of time on tweaks which are of the nature that one has to ask, "...am I hearing a difference or not?" If it's a beneficial change/noticeable change it has to be discernable immediately, or else what's the point? When changing cables or jumpers, the difference on a good system should be such that one notices it immediately. The issue of whether it's preferred sound longer term can take a while, but the question of "does it make a difference" should take less than 120 seconds.
How about this? Does polishing a CD make a difference in how it sounds? Before you say "it can't" why don't you try it? If you've got more than a Denon receiver and Radio shack speakers, you'll likely hear the difference. If you have a high end system and don't hear a difference, I'm sorry to tell you... you have hearing loss.
I find it incredible that in this age of nanotechnology, molecular biology etc, where it is demonstable that minute variations can have critical impact many are holding antiquated beliefs that physical changes (is changing a calble from 16 Ga to 8 Ga, and from stranded to solid core enough of a change?) on such a relatively huge scale don't make a difference.
