The digital audio out is to connect to a receiver. In this case, your overture is your "receiver." You will need a digital to analog converter, such as:
http://www.amazon.com/Gefen-GefenTV-Digital-Analog-Decoder/dp/B0021QBIBQ/ref=sr_1_1?ie=UTF8&s=electronics&qid=1263408043&sr=1-1-spell
Then, you will need the RCA to DIN connecter I mentioned from the converter.
HOWEVER, you can see on your manual that you linked that you have RCA (red and white) audio out! So, you don't need the converter in that case!
Then, you set your Overture to AUX and then whatever is playing on your TV will play on your overture.