Hi,
I use the amp circuit so that I can power a PC Speaker directly from the Arduino without needing an MP3 dock or anything else.
I have used the simple Resistor/Capacitor circuit in the link below (from digital pin 6 to the Audio out jack) to output sound without amplification - for example to send sound output from the Arduino into the aux input of an MP3 dock or similar equipment.
I am far from expert though so others might have better suggestions -
Duane B