A few thoughts: It could just be time and a few more weeks will help, although I suspect not. The idea of using different power leads as tone controls might work but you really need to try different ones because only your ears can tell about the results.

Have you got a sub woofer or two in the system? It's worth trying a high crossover - 80Hz - to a mono sub (or stereo subs) and relieving the 5200s of bass delivery. That helped with my old 5000s.

Steve

Steve