also, the mega has a whole 15 Analogue ins, so ignore the bit about reducing it to 5.
or, you could put one single input in to start with, then try and make it do something simple.
the add inputs to it one by one.
the simplest one is going to be:
Read the analogue value coming in on A1
express the value as the brightness of a single LED.
In the arduino IDE click: File, Examples, Analog, Analog input.
all you would do is replace the Potentiometer with your audio input.
i presume you would need to be careful not to over cook the arduino (too much volume would cause too much voltage perhaps?)