As a previous CAP-151 owner I would say upgrade the amp. I was happy with my Classe until I sold it a was thrilled with the change. The Classe seemed lifeless in retrospect. The Bel Canto eVo2i which replaced the Classe more than two years ago is still in my system.
Never heard the Concentra so can't comment on it's sound. Good luck whichever way you go.
Never heard the Concentra so can't comment on it's sound. Good luck whichever way you go.