How to improve Jitter issue via USB/ETHERNET ?

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Gui, as I said earlier, I don't think you're making up the fact that you hear differences - and I hope I didn't give that impression.  I do feel that ascribing what you hear to jitter is misleading unless you have objective evidence that jitter in the specific, technical sense is truly the cause.  To put it more clearly, you could replace the word "jitter" in your previous post with the word "badness" and (I believe) it would not change what you're actually communicating to anyone else.

Actually I don't think whether or not I can hear differences between cables is relevant, for these reasons: firstly, I haven't argued that I can hear such differences, and secondly, if I were to hear any I feel that the most likely cause (at least for me) would be due to what's subjectively going on in my head rather than what's objectively happening in the cable.  Thirdly, I prefer not to get into "my ears/system are better than your ears/system" discussions.

Since you asked my opinion on the topic: I believe that there may be cases where cables can make a difference, depending on the interface and the specific devices at each end.  From what I've read the most likely objective, potential causes of sound quality differences in USB and Ethernet cables seem to be things like noise transmission, ground currents and possibly EMI/RFI.  These effects are probably so sensitive to the exact system set-up that what works well in one system will not work well in another, so it's more or less impossible to generalise from any individual experience.

However, this sounds like digging rather hard to find something to pin a sound quality difference upon.  If the difference is repeatable in a well-designed test then that might be justified, of course.  But I don't think it's necessary to resort to anything as esoteric as that when there's only anecdotal evidence or a sighted AB comparison.

You seem determined to keep psychoacoustics and expectation bias out of the discussion, but it can't be eliminated from the normal experience of listening (that is, outside a properly-designed experiment).  Our hearing is very easily fooled; just to pick one example, the McGurk effect shows how hearing can tell us quite different things depending on what we see.  This effect is not subtle, and it is very strong even when you know about it - it's just the way the brain works, like it or not.