Peter, don't spend money chasing cable upgrades until you figure out what is going on. In my experience, no cable change will fix a fundamental system problem, which is what it sounds like you have.
But do give the amp more time to break in. Do you have another amp you can try to see how much of the problem is directly related to having the Berning in the system?
But do give the amp more time to break in. Do you have another amp you can try to see how much of the problem is directly related to having the Berning in the system?