MarkT:
If you sample less frequently you'll get the audio spectrum aliased on top of itself to a lower bandwidth.This might be fine for measuring signal level, although you'd not be as precise due to the missing infromation.
The ideal is to put a peak detector circuit on the channels. Basically an opamp, diode and a capacitor, so the capacitor charges to match the highest voltage peak of the waves and discharges much more slowly, although we are talking about discharging within a few milliseconds.
So rather than having to sample at full 44Khz to find the peak of the wave, you just sample the capacitor at a much lower rate like 1Khz or even the display update rate.
From oscilloscope tests it works rather well, the tricky part is matching the capacitor and any parallel discharge resistor to the impedance of the ADC. I found the AVR ADC pulled the capacitor down rapidly, so I had to remove the parallel discharge resistor completely.