Negative voltages can indeed be unhealthy for an Arduino input, but that is usually fixed by pulling the voltage divider output up to mid-voltage (~2.5volt) with an extra resistor to VCC.
62VAC (175volt peak/peak) is rather high for an audio amp.
What sort of amp are we talking about. Car booster? Class-AB or class-D?
Single output or bridge-mode?
Leo..