AFAIK the Z560s do not have digital inputs, so you should use analog. Don't enable digital out only or else the analogs will be cut off. It makes no difference in the functioning of the digital connections. To get sound out of the rear speakers, hook up the secondary/surround/rear (I don't know the label of them as I don't own Z560s) to the Line-Out on the Audigy then go to the Surround Mixer and set Speakers to 4 Speakers.