I thought nothing could improve on my beloved Shure SE535 earphones. I said the same in my review of the Comply earbuds, which did indeed enhance the already fine sound of the Shures.
But replacing the Shure cable with the FiiO has delivered a quantum leap in sound quality. It really feels as if the music is taken straight from the studio and dropped off unchanged into my head. Every voice and instrument shines clear and distinct. I can't wait to play new tracks as well as old familiar ones to see how they will sound. The cable also seems to be of solid construction, is comfortable to wear and looks a treat.
If you have a premium set of phones, do your ears a favour and upgrade the cable!