Not to worry, the amp did not do this to the wires. I have the exact same wires and use them in a system in my garage and in my three season room. Both runs of wire experience this "burn" look. After I cut the ends off and peeled back the covering, it was evident it was oxidation. I contacted monster and they said it wouldn't degrade the sound but would warrant the wires if I returned them. Since I am using them in the garage and in the three season room I thought I would just leave them in place.
Call monster and they will tell you what to do if you want to return them.
Later,
L