lol, even 4awg will cook in time, and still not pass current well....... hand him a straw and tell him to yell through it for a min. no breathing through his nose, or around the straw. then, hand him something like a 2"+ vacuum hose, or shipping tube and do the same... that is what the amp is seeing. the 8awg is only good for like 40a, depending on length, and over that, the voltage does drop, and the power supply circuits see a lot of heat from it, which also transfers over to the outputs, so yes, it can damage the amp. unless he plans on dropping under 400watts to justify using the wire, then time to upgrade.