These are two zener regulators and the corresponding ballast resistors. They may get (very...) warm. If the voltage is on spec, the charring should be tolerable. Actually, you don't need that high temperature to cause the observed kind of discoloration over a few years' time. One thing that would worry me much more are the electrolytics in close proximity of the "hot" resistors. This kind of arrangement can almost be considered to be "planned obsolescense" since the caps will dry out over a few years and become high-ESR. This may or may not cause additional trouble, depending on their usage. I'ld probably simply go and replace them all, they are small enough to be no-brainers price-wise. Preferably, you should use 105°C rated types as replacements. Just noticed -- in the second photo, you already removed some. Right so!
Did you check the mains voltage present at you friend's home (also for surges)? Often, this consumer electronics isn't designed for a high margin of mains overvoltage. This may also contribute to too much dissipation in these shunt regulators and possibly contribute to the failure of the output stage. The reported 110V total supply voltage to the power amps appears a little high as well, though only marginally.