I wouldn't upgrade to the Essence from your Cornwalls if you listen to hard rock and metal. The Essence sound better with lighter type music. I would though upgrade to the Omen Defs since these are dynamic and have a more raw sound that would do well with rock and metal. Your Cayins are plenty enough to drive the omen defs to crazy volumes.
Zu Audio Essence vs Klipsch Cornwall
I'm currently running Cornwall's with a Cayin A88-t a thorens TD-125 mk2 with an SME arm and shure cart. I've been looking at trying Zu products for awhile but just don't know if they would be a better choice than the Cornwalls. I listen to mainly Hard rock and metal.I really like the old Klipsch speakers but I would like something thats better from top to bottom at lower volumes.